Land warfare

This page deals with combat mechanics. For information on the recruitment and maintenance of armies see army. For the individual unit types see land units.

Land warfare is the deployment and maneuvering of military assets against an enemy, in most cases this results in combat between opposing armies. In EUIV most combat is land-based and, while the naval aspect of war holds importance, losing the land war is usually the main cause of defeat. The art of land warfare is therefore of significant importance, and its complexities are discussed here as fully as possible.

Combat interface

The conclusion to a normal land battle.

Combat is not only determined by mere numbers such as modifiers and dice-rolls, but through a complex simulation in which units deployed into two rows of positions for each side, allowing units to fight the enemy units in front of them, the enemies at their flanks if possible (with high enough flanking range), and move between different positions if needed. All the while, the system retreats destroyed or low-morale units and deploys reinforcements and reserves as well.

The combat system, while not being entirely obvious or intuitive, can be seen through the combat interface which allows the player to see which regiment is fighting which, and which is moving where.

Terrain

Terrain map. Border pixels belong to the province to their southeast.

Terrain for each province is shown in both the terrain and simple terrain mapmodes. Terrain shows a natural-looking map, while simple terrain color-codes each province by its terrain type; both have tooltips showing terrain type, fort level, and the current winter, if any. Some terrain imposes a movement speed penalty to armies traveling in the province in addition to a negative rough terrain modifier to the attacking army, with different types of terrain having different modifiers.

Here is a list of the types of terrain and the modifiers which they grant.

Terrain	Supply limit	Local defensiveness	Movement cost	Attacker penalty	Local development cost
Glacial	+2		+25%	−1	+50%
Farmlands	+10		+10%		−5%
Forest	+4		+25%	−1	+20%
Hills	+5	+10%	+40%	−1	+25%
Woods	+6		+10%	−1	+15%
Mountain	+4	+25%	+50%	−2	+35%
Grasslands	+8
Jungle	+5		+50%	−1	+35%
Marsh	+5		+30%	−1	+25%
Desert	+4		+5%		+50%
Coastal Desert	+4				+35%
Coastline	+6				+25%
Drylands	+7				+5%
Highlands	+6	+10%	+40%	−1	+20%
Savannah	+6				+15%
Steppes	+6				+20%

Crossing penalties

A crossing penalty that reduces all dice rolls is applied to the attacker under the following circumstances:

• Crossing a river: −1 to all rolls.

  The presence of a river in between a province and its neighbors is indicated in the province window, through a small river icon. Mousing over this icon will show which neighboring provinces require a river to be crossed in order for an army to reach the province.

• Crossing a strait: −2 to all rolls. See straits for a list.
• Amphibious landing: −2 to all rolls. This includes an attack from sea or a landing directly with ships at port.

For attackers that originate from multiple provinces, they will all receive the crossing penalty if any one of them would normally receive it alone. All crossing penalties are removed if the attacking leader has a higher maneuver rating than the defending leader. The check on leader maneuver rating is performed daily, so a high maneuver leader can still swing the tide of battle even if he joins an engagement late.

Battles in a province under siege

Normally, the "attacker" is defined as whichever side moves into a given province last, while the "defender" is whichever one was already occupying the area. However, if a given army is besieging a province that contains a fort and is attacked by troops owned by or allied with whoever currently controls the fort, the roles are switched: the siege army is treated as the "attackers," and those attempting to break the siege are the "defenders." Attacker penalties from terrain are applied to the siege army, while attacker penalties from river/strait crossings are nullified regardless of any leaders' Maneuver pips.

The player can take this into account when building forts, as well as when choosing which provinces to siege and which besieged provinces to prioritize sending their troops to. Also note that this only applies to provinces with forts.

If a sieging army wins a battle on a province where they're sieging, an immediate bonus siege tick is triggered. This does not reset the ticking down for the next siege tick.

Deployment

Army composition

Main article: Army#Composition

To maximize the effectiveness of an army, a proper mixture of troops is important.

Combat width

Combat width determines how many units can actively participate in a battle at one time. For every 1 combat width, 1 additional regiment can be placed in the front and back rows, if sufficient troops are available. The base combat width is 15. As military technology advances, a country's combat width increases, allowing them to use more soldiers effectively at once. All countries other than Native Americans start with tech level 2 or 3, so their starting combat width will be 20. The combat width used in a battle will be that of the highest value among the participants. Here is a table of combat width by military technology level.

Military technology level	0	2	5	6	9	11	14	16	18	20	22	24	26
Combat width	15	20	22	24	25	27	29	30	32	34	36	38	40

Unit deployment

The game uses an undocumented algorithm to automatically deploy land units on the battlefield for each side of the battle. Through observation and controlled experiments, the community has suggested a theory that the game seems to follow, dependent on the rough size and composition of each army.

For the smaller army

• If there is not enough infantry to fill the entire first row, the game will prioritize to:
  1. Deploy all infantry in the first row.
  2. Deploy as much cavalry as possible to the sides of the first row.
  3. Deploy all artillery in the second row. If there are more units in the second row than the first, then it will redeploy artillery to the first row until both rows are even.
  4. If there is still space remaining in the second row, deploy all remaining cavalry onto the second row, beginning from the edge of the first row then inwards.

• If there is enough infantry to fill the entire first row, the game will prioritize to:
  1. Deploy all infantry in first row, except for X^{[Unknown value]} positions to each side.
  2. Deploy X units of cavalry on each side of the first row.
  3. Deploy all artillery on the second row.
  4. If space is left on the second row, deploy all remaining infantry in the second row next to the artillery, except for Y^{[Unknown value]} positions to each side.
  5. Deploy all remaining cavalry in the second row, beginning from the edge and going inwards.

For the bigger army

For an army bigger than the combat width, the game will prioritize to:

1. Deploy all infantry in the first row that can be positioned to attack enemy units in the first row, except for X^{[Unknown value]} positions to each side.
2. Deploy all cavalry in the first row that can be positioned to attack the enemy units in the first row.
3. Deploy all artillery in the second row.
4. If space is left in the second row, deploy as much infantry in the second row besides the artillery as there are positions available behind the infantry in the first row.
5. If space is left in the second row, deploy as much cavalry in the second row besides the infantry as there are positions available behind the cavalry in the first row.

Combat sequence

When two hostile armies meet in a province a battle will commence. A battle will last until one side is routed or annihilated.

Phases

Combat is divided into a series of 3-day phases. Phases alternate between Fire and Shock, with the Fire phase happening first.

Target selection

Units in the front row can attack any enemy unit within their horizontal flanking range. Normally they will only engage enemies that are directly ahead of themselves, but they can sometimes execute flanking attack regardless if it will be more effective at reducing the enemy's combat ability. This typically occurs if the unit is facing an enemy artillery regiment or a particularly outdated unit; in this case the unit may choose to attack the flanks of a stronger enemy unit nearby. Artillery are the only units that can attack from the back row, but they will only deal 50% damage from that position.

Dice roll

At the beginning of each phase, each side rolls a die. The result is used to determine the morale damage and casualties inflicted to the opponents each day in the three-day-phase.

The result is computed as following:

$D_{result}=D_{roll}+Ls_{Atk}+Up_{Atk}-(enemy)Ls_{Def}-Up_{Def}-T_{mod}$

• Dice roll ($D_{roll}$): Is a random number between 0-9, rolled for each entire side at the beginning of each phase (not each day).
• Leader skill ($Ls$): The leader skill for that phase (Fire or Shock Pips).
• Attacking unit attack pips ($Up$): The attack pips for the attacking unit for the current phase, or Morale pips if computing morale damage. Note all units attack during every phase---here "attack" does not refer to which army is attacking.
• Defending unit defense pips: The corresponding defense pips for the defending unit.
• Terrain modifiers ($T_{mod}$): Harsh terrain may give a penalty to the attacks of the attacking army (in this case "attack" refers to the attacking side).

Casualties

Each day, two casualties computations occur, one for actual casualties using units' fire or shock pips (depending on the day's phase) and a second for "morale casualties" (the casualties value used in the morale damage formula) using units' morale pips:

$C = C_{base}\cdot Us_{Atk} \cdot Um_{Atk} \cdot (1+ CA_{Atk})\cdot \frac{Ud_{Atk}}{Ut_{Def}}$

• Base casualties ($C_{base}$): Base casualties are determined by the dice result according to the following formula:

$C_{base} = 15 + 5 \cdot D_{result}$

• Attacking unit strength ($Us_{Atk}$): If the attacking unit has less than its maximum of 1000 men, damage will be reduced proportionally.
• Attacking unit modifier ($Um_{Atk}$): Determined by unit type and military technology level and. See Technology#Cumulative mil tech effects to army.
• Attacking unit Combat Ability ($CA_{Atk}$): Any Combat Ability bonuses the attacking unit has.
• Attacking unit Discipline ($Ud_{Atk}$): The Discipline of the attacking unit. Note that Discipline does also increase Military Tactics, so it increases defense indirectly.
• Defending unit Tactics ($Ut_{Def}$): The Tactics of the defending unit.

There are several unique national ideas which modify the amount of damage inflicted and received in both the fire and shock phases.

Various conditions and ideas that increase fire damage dealt:

	Conditions
+20%	with ‘French Musketeers’ splendor ability (only France during Age of Absolutism)
+10%	for Streltsy regiments with a general which has the ‘Ruthless’ leader trait
0 − +10%	depending on army professionalism

	Traditions	Ideas	Bonuses	Policies
+10%	—	Date idea 4: Dragon Corps Dutch idea 7: Platoon Fire English idea 5: Redcoats Jaunpuri idea 1: Purbias Hatakeyama idea 7: Sakai-shu Hindustani idea 5: Gunpowder Empire Ilkhanid idea 7: Recruit Turkoman Gunners Isshiki idea 5: Inadome Gunnery Mewari idea 6: Mandatory Firearm Drills Münster idea 6: Bommen Berend Mysorean idea 5: Rockets! Oda idea 5: Triple Firing Rajputana idea 4: Purbia Legacy Shimazu idea 5: Tanegashima Smolenskian idea 2: The Armories of Smolensk Texan idea 2: Texan Revolution Tirhuti idea 4: Purbias Utsunomiya idea 2: Legacy of Nasu no Yoichi	Beninese ambition Dhundhari ambition	—

Ideas that increase shock damage dealt:

	Traditions	Ideas	Bonuses	Policies
+15%	—	Highlander idea 5: Highland Charge	—	—
+10%	Muscovite traditions	Great Yuan idea 4: Keshik and Weijun Nagpuri idea 5: Light Cavalry Shock Tactics Nanbu idea 6: Chosonji Temple Timurid idea 3: Unleash the Tiger	Cossack ambition	—

• +5% Assimilating Celtic culture group as Mughals

Ideas that reduce fire damage taken:

	Traditions	Ideas	Bonuses	Policies
−15%	—	Andalusian idea 1: Stand Against the Reconquista	—	—
−10%	Texan traditions	Hanoverian idea 7: King's Legion Leinster idea 4: He Who Is Not Strong Must Be Cunning Russian idea 7: Broaden the curriculum of the Cadet Corps	—	—

Ideas that reduce shock damage taken:

	Traditions	Ideas	Bonuses	Policies
−15%	—	Ando idea 1: March of Akita Rassid idea 5: Mountain Strongholds	—	—
−10%	Ayyubid traditions Dithmarscher traditions Manipur traditions Orissan traditions Sistani traditions Yi traditions	Assamese idea 3: River Warfare Baluch idea 2: Hani and Sheh Mureed Hausan idea 5: Sarkin Yaki Irish idea 1: Irish Endurance Kanem Bornuan idea 5: Fixed Military Camps Lur idea 1: Kingdom in the Zagros Mountains	Butua ambition	—
−5%	—	Bohemian idea 3: Wagenburg	—	—

• −10% Defensive Planner leader trait

Morale damage

$M_{dam}=Casualties\cdot Morale/1000$

• 6 base casualties translates to dealing 1% of the attacking unit's maximum morale as morale damage. Note that the modifiers may be different. Units also use their morale pips, but the pips added by the general still use shock and fire pips during the shock and fire phases respectively.
• Attacking unit maximum morale ($Morale$): Note that this is the maximum morale of the attacking unit, not the current morale.
• After recent observations and a combat tooltip, it appears that the tech level multiplier to shock and fire damage affects morale damage as well.
• There is an additional contribution that also affects units that are deployed, but not actively participating in combat

Combat statistics

Military tactics

Military tactics reduces the amount of damage a country's troops take in combat. Military tactics is increased by military technology. It is also multiplied by discipline.

Military technology level	0	4	6	7	9	12	15	19	21	23	24	30	32
Military tactics	0.5	0.75	1.0	1.25	1.5	1.75	2.0	2.25	2.5	2.75	3.0	3.25	3.5

Pips

Each military unit has offensive and defensive stats in three categories: fire, shock, and morale. Offensive stats are represented by yellow pips, and defensive stats by green pips. During each combat phase, each unit will use its offensive pips to increase damage dealt, and its defensive pips to mitigate damage received.

This implies that offensive pips are recommended if the player fields a larger army than their opponent, and vice-versa for defensive pips. This is because a larger army with higher combat width will have a larger surface area of attack. If, say, the enemy has an army with 10 infantry and 10 artillery, and the player only has 10 infantry. The player will suffer significantly fewer casualties with defensive fire pips, because it will reduce damage from both infantry and artillery fire. Conversely, if the player has a larger army, they would want higher offensive pips on their infantry and artillery because they have 2 attacking regiments for every defending enemy regiment.

The recommended pre-artillery composition with no regard to cost, consists of high proportions of cavalry and a high shock pip Leader, as tier 1 cavalry has 1 shock and 0 fire modifier, and tier 1 infantry has 0.35 fire and 0.5 shock modifier. Combined with a shock Leader, the player will inflict significantly more damage during the shock phase. This also means that defensive shock pips are recommended early game to defend the player's army from the enemy's shock damage.

After military technology level 7 , the combined fire pips of tier 2 infantry and tier 1 artillery balance fire and shock pips, for both Nomadic and Civilized nations. If the player plans on recruiting an amount of artillery units equal to the length of the current combat width, a fire pip Leader is now recommended.

Flanking range

Flanking range determines the horizontal range in which a unit may make a flanking attack. The base flanking range is 1 for infantry, and 2 for cavalry and artillery. There are military technologies which increase the flanking range of units as the game progresses. Below is a table with said military technology levels and how much they increase flanking range.

Flanking range

0	0	1	2	2
10	+25%	1	2	2
18	+50%	1	3	3
23	+100%	2	4	4
28	+125%	2	4	4
30	+150%	2	5	5

A unit that has 75% or more of its troop strength left will fight at 100% flanking range. If they are in between 50 and 75% of their strength, they will fight at 75% flanking range. When between 25 and 50% strength they will fight at 50% of their flanking range.

Unit strength	Flanking range
1000–750	100%
749–500	−25%
499–250	−50%
249–0	−75%

The final range is always rounded down to the nearest integer.

Several ideas give increased cavalry flanking range:

	Traditions	Ideas	Bonuses	Policies
+50%	—	Albanian idea 4: Hit and Run Clanricarde idea 4: Irish Hobbies Deccani Sultanate idea 5: Bargi Giri Lan Na idea 6: Elephant Charge Mossi idea 2: Cavalry Raids Najdi idea 5: Arabian Horsemanship	Ilkhanid ambition Kazani ambition	—
+25%	—	Arabian idea 2: Arabian Horses	—	—

• +20% Assimilating Evenki culture group as Mughals

Morale

Morale is an important factor in fighting battles. Each day of combat a unit will take a Morale hit of 0.01 or 0.02 regardless of damage taken from an enemy regiment. If it is taking casualties from an enemy, additional morale damage will be inflicted. Once an army's overall Morale value has been reduced to zero the army will attempt to retreat. Retreat cannot happen until both two fire and two shock phases have completed, so an army that has its morale reduced to 0 before that point will be destroyed. This destruction is known as a stackwipe.

A unit that has its morale drop below 0.50 is flagged as disorganized, which is indicated by a small flame next to its morale bar on the map and interface. A disorganized army is unable to start moving until its morale has recovered above 0.50. Newly trained regiments at low land unit maintenance will often fall below this threshold.

If an army loses a battle while having low enough morale to be disorganized, they will be forced to retreat to a controlled province (owned, allied in war, or occupied by player or allies). This province can be very far away from where the battle took place. They will prioritize to retreat to a province with high development, a fort, and no adjacent enemies. While retreating, it cannot be engaged in combat or controlled until it reaches the safer province (or in extreme circumstances if it recovers to 100% morale before reaching the destination). The army also moves slightly faster, and will recover morale at a normal rate during the retreat. If there are no available controlled provinces to retreat to within a large range, the army will shattered retreat to one province away. The army can then be immediately re-engaged, often with very low to even no morale, if a monthly tick has not yet completed. This can be devastating as an offensive tactic, but may also affect the player as well.

A controlled retreat is manually ordering an army to retreat from battle after the initial fire and shock phases, and while it still has greater than 0.50 average morale. This allows the player to control the destination of the shattered retreat. If the morale of an army is less than 0.50 the player can not control the destination. If multiple armies have converged into a battle, it is possible that some armies will have enough morale for a controlled retreat, while others may not (often the initial stack in the battle).

Winning a battle gives the winning armies 50% of their maximum morale and retreating from a battle will reduce the other allied armies' morale relative to the portion of troops leaving the engagement).

After a battle is fought, an army must spend some time without fighting for its morale to recover. The normal morale recovery on the 1st of every month can not occur while in combat.

• A shattered army will get an extra morale bonus once it stops retreating
• Morale is not gained while forced marching

Modifiers

The following modifiers contribute to the maximum morale of a nation's army:

• Army Maintenance: Ranging from 0.51 at minimum maintenance to the defined maximum at maximum maintenance.
• Ideas and policies:

	Traditions	Ideas	Bonuses	Policies
+20%	—	French idea 2: Elan! Prussian idea 3: Army Professionalism	—	—
+15%	Andalusian traditions Castilian traditions Nagpuri traditions Spanish traditions	Defensive idea 2: Military Drill Air idea 2: Cross of Agades Highlander idea 1: The Wallace Polish idea 7: Focus on Field Defenses	Texan ambition	—
+10%	Aq Qoyunlu traditions Austrian traditions Ava traditions Beninese traditions Burgundian traditions Butua traditions Chernihiv traditions Client State traditions Deccani traditions Dhundhari traditions Dithmarscher traditions Hatakeyama traditions Hojo traditions Huron traditions Irish traditions Khorasani traditions Liège traditions Moldavian traditions Mysorean traditions Nepalese Princedom traditions Oda traditions Ogasawara traditions Pacific Northwest traditions Persian traditions Pomeranian traditions Provençal traditions Punjabi traditions Rajputana traditions Rûmi traditions Transoxianian traditions Tsutsui traditions Welsh traditions	Plutocratic idea 2: Abolished Serfdom Ajami idea 3: Legacy of the Ilkhans Amago idea 4: Ten Brave Warriors American idea 4: Lessons of Valley Forge Aragonese idea 7: Protect the Little Folk Ardabili idea 1: The Safavid Order Aymaran idea 5: The Tinku Rites Ayyubid idea 3: Righteousness of the Faith Aztec idea 4: Eagles and Jaguars Bulgarian idea 6: Military Flexibility Carib idea 3: Resistance towards the Pailanti'po Catalan idea 6: 'Lliures o Morts' Cebu idea 1: Lumaya’s Ambition Chachapoyan idea 1: Warriors of the Clouds Charruan idea 6: Garra Charrua Cherokee idea 5: Ghigau Chiba idea 2: Dream of Masakado Creek idea 7: Red Sticks Daimyo idea 4: The Five Rings Desmondian idea 3: Gaelic Bastion Finnish idea 7: The Anjala Conspiracy French ducal idea 7: La Petite Nation Frisian idea 3: Dutch Courage Fulani Jihad idea 4: Imans and Emirs Galician idea 5: Santiago y Cierra! Garhwali idea 3: Martial Diplomacy Gelre idea 5: The Gelderland Wars Great Yuan idea 2: A Savage Kingdom Holy and Enchanted Imerina idea 2: The Twelve Sampys of Imerina Ionian idea 1: Frankokratia Kangra idea 3: Martial Heritage Khmer idea 1: Preah Ko Preah Keo Kikuchi idea 4: Fortify the Domain Kildarean idea 3: Silken Thomas Krakowian idea 1: Legendary Legacy K'iche idea 6: K'iq'ab's Vengeance Luban idea 4: Encourage the Kasala Tradition Lur idea 6: Rise of the Lurs Manipur idea 2: Martial Traditions Mayan idea 7: Caste War Medri Bahri idea 5: Independent Traditions Mexican idea 7: Grito de Delores Miao idea 3: Unity of the Tribes Mindanao idea 6: Guerrilla Warfare Muscovite idea 4: Pomestnoe Voisko Mushasha idea 1: Fervent Millenarianism Nanbu idea 1: Genji in the North Native idea 1: Counting Coups Neapolitan idea 4: Crush the Power of the Barons Nepali idea 5: The Royal Kumari Nivernais idea 4: True Frenchmen Pegu idea 4: Ramannadesa Rassid idea 1: The Living Imam Sadiyan idea 1: Land of Glory Samtskhe idea 4: Independent Ambitions Semien idea 1: Legacy of Queen Judith Serbian idea 7: Balkan Hajduks Shiba idea 4: Atsuta Shrine Shimazu idea 1: Satsuma Hayato Shoni idea 2: Defender of Japan Slovak idea 7: Slovak National Awakening Songhai idea 3: Jihad Against the Pagans Takeda idea 1: Leader of Kai Genji Timurid idea 2: The Mantle of the Great Khan Tokugawa idea 1: Mikawa Bushi Trebizondian idea 5: The Lessons of the Fourth Crusade Uesugi idea 4: Dragon of Echigo Yarkandi idea 5: Holy Warriors Yi idea 7: Children of the Black Tiger	Ajuuraan ambition Athenian ambition Circassian ambition Colonial ambition Cornish ambition Dai Viet ambition Kievan ambition Kitabatake ambition Ryazan ambition	Religious-Quantity: Field priests and Soldier's prayer books
+5%	—	Russian idea 7: Broaden the curriculum of the Cadet Corps	—	Quality-Religious: The Military Zeal Act

• Researching military technology:
  • Military technology (0): +2.0
  • Military technology (3): +0.5 (cumulative +2.5)
  • Military technology (4): +0.5 (cumulative +3.0)
  • Military technology (15): +1.0 (cumulative +4.0)
  • Military technology (26): +1.0 (cumulative +5.0)
  • Military technology (30): +1.0 (cumulative +6.0)

Various National bonuses:

• Prestige: +10% at 100 Prestige, -10% at -100 Prestige
• Power Projection: +10% at 100 Power Projection
• Army reformer advisor: +10%
• Army tradition: +25% at 100 tradition
• Being the Defender of the Faith: +5%
• Piety (Muslim only): +10% at 100 Mysticism

Religion:

• Shia: +5%
• Protestant Church aspect "Saints accept Prayers": +5%
• Reformed "War" focus (requires Wealth of Nations DLC) +10%
• Vajrayana: +5%
• Shinto: +10%
• Sikh: +10%
• Inti with "Expanded Mitma Policy": +10%
• Nahuatl: +10%
• Tengri with either Shia, Nahuatl or Sikh as syncretic faiths: +5%

Government:

• Noble Republic: +10%
• Revolutionary Empire: +10%
• Daimyo: +10%
• Merchant Republic with "Aristocrats" Faction in power: +5%
• Republican Dictatorship: +10%
• Revolutionary Republic: +10%
• Ambrosian Republic: +5%
• Peasants Republic: +5%
• Assimilating Japanese culture group as Mughals: +10%

Morale recovery

Every month, a regiment recovers 15% of its maximum morale. The following contributes to a nation's morale recovery speed.

• Regiment is in home territory: +5%
• Army tradition: +10% at 100 tradition
• When commanded by a leader with the Inspirational Leader personality trait: +10%
• Various events, decisions, and modifiers
• Armies that win battles will gain a significant boost to morale, to prevent situations where an army is stack wiped due to winning a narrowly fought battle and then immediately being attacked. The amount of morale regained depends on the strength of the enemy army defeated relative to their own strength.
• Certain ideas and policies as follows

	Traditions	Ideas	Bonuses	Policies
+15%	—	—	—	Quality-Administrative: The Liquor Act
+5%	Armenian traditions Fulani traditions Hungarian traditions Ryazan traditions	Pskovian idea 2: Legacy of Daumantas	Fully Offensive Persian ambition	Expansion-Defensive: Local Army Organization Religious-Quantity: Field priests and Soldier's prayer books

Cavalry to infantry ratio

Armies exceeding their nation's ratio of cavalry to infantry receive the "insufficient support" penalty which applies a −25% military tactics to those armies until their ratio has been restored to normal. This ratio threshold is checked daily even during battles, and is based on the actual headcount of individual soldiers instead of regiments. Since infantry tends to take more casualties than cavalry, it is advisable to take at least a bit more infantry than the ratio would suggest.

The base cavalry to infantry ratio is 50%. This is further modified by the following:

	Traditions	Ideas	Bonuses	Policies
+10%	—	Polish idea 4: Winged Hussars	—	—

• +25% Has a Steppe Horde government
• +25% Has a Tribal Federation government
• +25% Is Tengri (with no syncretic faith)
• +20% Has Cavalry Armies ability (an Age of Discovery only ability)
• +10% Is Sunni
• +10% A loyal Cossacks estate (max value)

Forts

Forts are used to protect a nation from invading armies.

Fort level and garrison

The following modifiers affect fort level:

• Capital province: +1 fort level for the capital province
• Fort buildings: +2 fort level per building level.

Each fort level increases the garrison of the province by 1000. Maximum garrison size is also influenced by the following ideas and policies:

	Traditions	Ideas	Bonuses	Policies
+25%	Desmondian traditions Highlander traditions Isshiki traditions Rigan traditions	Quantity idea 6: Conscripted Garrisons Ming idea 1: Nine Garrisons of The Great Wall Toki idea 4: Strategic Castles	—	—
+20%	—	Betsimisaraka idea 1: People of the Coast	—	—
+10%	—	Divine idea 5: Onward Christian Soldiers Garhwali idea 2: Himalayan Kingdom Italian idea 4: Trace Italienne Kangra idea 4: Control of the Hill Forts Slovak idea 4: Land of Castles	—	Innovative-Quantity: The Garrison System

Garrison recovers monthly at a base rate of 5% plus 1% per base manpower of the province. The rate is also increased by the following ideas and policies:

	Traditions	Ideas	Bonuses	Policies
+25%	Ito traditions Luxembourg traditions Meath traditions Pueblo traditions	Clevian idea 7: Militarize Schwanenburg	—	—
+20%	Toki traditions	—	—	—
+15%	—	Austrian idea 2: Military Frontier	—	—
+10%	—	Divine idea 5: Onward Christian Soldiers	—	Influence-Quantity: Guerilla Warfare

Fort maintenance

Each building level of fort costs 1 ducat per month. Forts can be mothballed by the nation that controls them; mothballing will reduce the fort maintenance by half but remove fort level and the current garrison from the city. A fort cannot be mothballed or de-mothballed while the city is under siege. The garrison will recover at a normal rate after mothballing is cancelled. Capital cities always have fort level at least 1, which stacks with any fort building in the province; this free fort level does not extend a zone of control, does not cost maintenance, and cannot be mothballed. A fort building in a capital province can be mothballed as normal, but the free fort will remain.

Mothballed or not, fort maintenance can be reduced by following modifiers:

	Conditions
−20%	with ‘Monastic Order’ government reform.
−10%	with ‘Sidhi Recruitment’ government reform. with parliament and active issue ‘Tax Provinces for Fortifications’. as march.
−10% − +10%	with Rajputs estate depending on their influence and loyalty.
+1%	for each percentage point of inflation.

	Traditions	Ideas	Bonuses	Policies
−20%	Lur traditions Meath traditions Ming traditions Vindhyan traditions	Estonian idea 3: Castles of Estonia French idea 5: Vauban Fortifications Ladakh idea 2: Fortified Mountain Cities Muscovite idea 6: Zasechnaya Cherta Odoyev idea 6: Fortification Efforts Somali idea 2: Qalqads Swiss idea 3: Alpine Defensiveness	Sligonian ambition	Innovative-Quantity: The Garrison System
−15%	Gujarati Princedom traditions	Northumbrian idea 4: A Land of Castles Luxembourg idea 4: The Fortress of Luxembourg Orleanaise idea 1: Sieges of Orleans Telugu idea 4: Great Forts of the East	—	—
−10%	Baden traditions Baluch traditions French ducal traditions Miao traditions Nizhny Novgorod traditions	Defensive idea 5: Defensive Mentality Ajami idea 5: Tribes of Iraq-e Ajam Austrian idea 2: Military Frontier Catalan idea 4: Fortifying Catalonia Kangra idea 4: Control of the Hill Forts Laotian idea 7: Laotian Hill Warfare Mutapan idea 3: Mutapa Architecture Nubian idea 7: Fortified Strongholds Semien idea 2: Mountain Kingdom Slovak idea 4: Land of Castles Tarascan idea 5: Fortified Frontier	—	Innovative-Defensive: Superior Fortifications

On borders towards rivals there are additional modifiers:

	Conditions
−100%	with ‘Protecting Forts’ ability in the ‘Age of Absolutism’.

	Traditions	Ideas	Bonuses	Policies
−50%	—	Expansion idea 4: Factories	—	Religious-Plutocratic: The Tolerance Act
−25%	—	Andalusian idea 7: Al Awasim	—	—

Zone of control

Main article: Zone of control

Active fort buildings (not counting the free fort level in the capital) provide a zone of control. A zone of control restricts the movement of enemy armies through the province with the fort, and provinces immediately adjacent to it. When an army enters a zone of control from a province not affected by a hostile zone of control the province it entered from is set as the 'return province'. In general the army can then only move to another province that has no more than one province that is not affected by a hostile zone of control between itself and the return province. The main exception to this rule is that the army can always move to a hostile fort. Please see the main article for full details as there are a number of exceptions and the behaviour is not intuitive.

Sieges

When hostile troops enter a province and stop moving, a siege/occupation will begin. To progress, the attacker requires a minimum of 3000 men per 1000 garrison. If the province has no garrison (whether because it has no fort or the fort's garrison is empty), 1000 men is enough and occupation is guaranteed within a month. Any unit types can be used for sieging, but for sieging a fortified province, only infantry will be used in an assault, and artillery speeds the siege up (see below). Progress in a siege will never decrease as long as attackers are continuously present; however, if all attackers leave the province, you will lose 1 siege status progress per day the province is unsieged.

Besieging armies will always take at least 1% base attrition, even if the province is unfortified. This rule only applies to enemy-owned provinces, however - when besieging friendly provinces to retake them from the enemy, this rule is ignored.

A besieging army always count as the attacker and will receive the province penalty and, depending on the way they entered the province, an additional crossing penalty when a battle takes place.

Sortie

The garrison can be ordered to make a sortie to fight the hostile army, at the cost of 10 military power. (The ‘Sortie from siege’ button is shown on the siege screen.) If the garrison army, which consists only of infantry, loses the fight the province and fort will become occupied. This can be used to win a battle in which both sides are evenly matched.

Phases

A siege progresses in phases. Each phase has a base length of 30 days and is modified by:

• Fort defense: +1% per defender's 1% fort defense and province defensiveness
• Siege ability: −1% per attacker's 1% Siege Ability
• Tactics difference: 6.25% per 0.25 military tactics difference to both sides. E.G. If the player's tactics is 0.5 higher than the enemy, the player's siege will be 12.5% faster and the enemy's siege will be 12.5% slower. Only the base tactics value counts, bonuses from discipline have no effect on phase time.

A siege dice roll is also triggered if the sieging army wins a battle on the besieged province.

Siege ability is influenced by the following ideas and policies:

	Traditions	Ideas	Bonuses	Policies
+20%	—	Offensive idea 5: Engineer Corps	—	—
+10%	—	Beninese idea 2: Isiatua Dutch idea 6: Army Sappers Highlander idea 3: Storming the Castle Ormond idea 6: Irish Siegecraft Otomo idea 7: Kunikuzushi Smolenskian idea 7: Tsar Mortars Utrecht idea 3: Fortified City	Luxembourg ambition	Innovative-Offensive: Modern Siege Weapons Quality-Religious: The Military Zeal Act

Various Modifiers:

• War exhaustion: −1% per point
• Army Tradition: +5% at 100
• Spy network: +20% at 100 (Requires Mare Nostrum)
• Tengri with Coptic syncretic faith: +10% (Requires The Cossacks)
• Hindu with Shakti as divinity: +5% (Requires Wealth of Nations)
• Army professionalism: +20% at 100 (Requires Cradle of Civilization)

Fort defense is influenced by the following ideas and policies:

	Traditions	Ideas	Bonuses	Policies
+25%	Georgian traditions	Afghan idea 2: Shadows of the Hindu Kush Bremish idea 6: Bremish Walls Cypriot idea 5: Cypriot Fortifications Divine idea 3: True Defender of the Faith Hamburger idea 3: Walls of Hamburg Jerusalem idea 6: Crusader Castles Knights Hospitaller idea 1: Defense of the Faith Theodorian idea 5: Mangup and Kalamita Forts Tyrconnell idea 1: Fort of the Foreigners	—	—
+20%	Albanian traditions Kildarean traditions Leinster traditions Mushasha traditions Odoyev traditions Orleanaise traditions Ormond traditions Slovak traditions Telugu traditions Tsutsui traditions Yi traditions	Defensive idea 5: Defensive Mentality Ainu idea 1: Chasi Ajami idea 1: Jibal Al-Haasa idea 4: Fortify the coastline Ayyubid idea 1: Citadels and Fortresses Barbary Corsair idea 5: Fortified Pirate Strongholds Breton idea 3: Breton March Caspian idea 6: A Safe Haven Chickasaw idea 6: Lessons of Ackia Couronian idea 1: Legacy of Sword Brethren Dai Viet idea 3: Autonomous Villages Dhundhari idea 1: Improve the Fort at Amer Ethiopian idea 3: Hostile Borders Galician idea 2: Galicia la Bella Hojo idea 5: Castles of the Hojo Hormuz idea 2: Protecting the Islands Ionian idea 2: Castles of the Angels Ito idea 5: Network of Forty-Eight Fortifications Krakowian idea 4: Casimirian Fortifications Lorraine idea 1: The Vosges Luxembourg idea 2: The Ardennes Malvi idea 4: Fortified Strongholds Maratha idea 2: Forts of Maharashtra Mazovian idea 2: Mazovian Frontier Meath idea 7: Siege Mentality Mindanao idea 5: Fortify our Ports Nivernais idea 5: Bridges of the Loire Offaly idea 5: Tower Houses Ogasawara idea 1: Shinano-Shugo Rigan idea 6: Fortify Riga Samtskhe idea 3: Fortresses of Samtskhe Savoyard idea 1: Repel the French Shirvani idea 2: Fortresses of Shirvan Thüringian idea 2: Fortifications of Erfurt Trebizondian idea 2: Pontic Mountains Tripuran idea 7: Strengthen Local Defenses Tverian idea 2: Defend Against Muscovy Ulster idea 7: Last Redoubt of Ireland Yamana idea 6: Isolated Heartland	Italian (cU) ambition Ladakh ambition Mesoamerican ambition Novgorodian ambition Permian ambition Rassid ambition Sumatran ambition	—
+15%	Aymaran traditions Carib traditions Kurdish traditions Mayan traditions Montenegrin traditions Muiscan traditions Transylvanian traditions	Amago idea 3: Fortified Strongholds Bosnian idea 7: Over the Hills and Through the Woods Chernihiv idea 4: Konotop Fortress Clevian idea 1: Walled Cities Client State idea 3: Fortified Border Danziger idea 6: Continued Independence Finnish idea 1: Expand Viborg Frisian idea 5: Flooding the Polders Fulani Jihad idea 2: Unrighteous Kings Garjati idea 1: Securing Our Defenses Gond idea 1: Securing Our Defenses Guarani idea 6: Repel the Bandeirantes! Imerina idea 4: Fortify the Highlands Kazani idea 6: Settle Down Khivan idea 6: Ichan Qal'a Kievan idea 3: Fending Off The Invaders Kikuchi idea 7: Central Stronghold Kutai idea 4: Anti-Piracy Measures Malagasy idea 1: Fortify the Coastline Mapuche idea 1: Mapuche Pucaras Mewari idea 3: The Fort of Kumbhalgarh Mossi idea 5: Land of the Ancestors Nepalese Princedom idea 5: Seize the Mountain Passes Nepali idea 2: Land of Peaks Provençal idea 4: Tarascon Castle Pueblo idea 3: Mesa Settlements Québécois idea 4: Fortifications of Quebec Rajput idea 2: Fortifying Rajputana Sadiyan idea 3: Hills and Jungles Siberian idea 4: Siberian Backwoods Siddi idea 3: Impregnable Island Fortress Shan idea 1: Fortified Cities Songhai idea 2: Independence from Mali Teutonic idea 5: Expand the Marches Vindhyan idea 2: Forts of the Vindhyas Yaroslavlyian idea 6: The Two Towers	Desmondian ambition Manipur ambition	—
+10%	Athenian traditions Dahomey traditions Pagarruyung traditions Sinhalese traditions	Andalusian idea 7: Al Awasim Andean idea 6: Hidden Cities Beninese idea 4: The Walls of Benin Chachapoyan idea 3: Summit Fortresses Cham idea 7: Resisting Foreign Rule Cherokee idea 6: Mountainous Isolation Chimu idea 2: Ciudadelas Garhwali idea 2: Himalayan Kingdom Holstein idea 1: Limes Saxoniae Kongolese idea 1: The Kongo River Basin Lan Xang idea 6: Merchants of Vientiane Navarran idea 1: Dorretxeak Nizhny Novgorod idea 4: Citadel Of Russia Polotskian idea 4: Land of Strongholds Tarascan idea 5: Fortified Frontier Tupi idea 7: Wall Builders Utrecht idea 3: Fortified City	Moldavian ambition	Espionage-Defensive: The Privy Council Establishment Act Influence-Defensive: Local Militias Innovative-Defensive: Superior Fortifications
+5%	—	Croatian idea 4: Antemurale Christianitatis Italian idea 4: Trace Italienne Ming idea 1: Nine Garrisons of The Great Wall Toki idea 4: Strategic Castles	—	—

Various Modifiers:

• Hindu with Vishnu as divinity: +20% (Requires Wealth of Nations)
• Norse with Tor as divinity: +10% (Requires El Dorado or a save converted from Crusader Kings II)
• mysticism as a Muslim: +20% from 100 Mysticism
• Coptic: +10%
• Defence Edict: +33%
• Lucky nation: +10%
• Certain events can temporarily increase siege ability or fort defense.

The mean number of phases to finish a siege for a particular starting bonus is as follows:

Starting bonus	−9	−8	−7	−6	−5	−4	−3	−2	−1	0	1	2	3	4	5	6	7	8	9	10	No fort
Starting success %	−100.00%	−92.86%	−85.71%	−78.57%	−71.43%	−64.29%	−57.14%	−50.00%	−42.86%	−35.71%	−28.57%	−21.43%	−14.29%	−7.14%	0.00%	7.14%	14.29%	21.43%	28.57%	35.71%	100%
Mean phases	43.18	30.51	25.24	21.44	17.42	14.75	12.65	10.87	9.41	8.20	7.24	6.48	5.78	5.13	4.52	3.86	3.27	2.82	2.46	2.17	1
Sieges per year	0.28	0.40	0.48	0.57	0.70	0.82	0.96	1.12	1.29	1.48	1.68	1.88	2.10	2.37	2.69	3.15	3.72	4.32	4.95	5.60	12

"Sieges per year" is computed at the default phase length of 30 days.

Dice roll

At the end of each siege phase, a die (1 to 14) is rolled. The following modifiers are then applied:

• Siege status. The most important modifier. As the siege goes on, this bonus will increase from its starting value of 0 depending on previous dice rolls. The maximum starts at 12 for a Castle or capital fort and is increased by 1 for each building level above a Castle, up to a maximum of 15 for a Fortress.
• Leader siege. If the attacking army has a leader, the leader's siege skill (+0–6) is added as a bonus.
• Artillery. Adding artillery to a siege will add a +1 to +5 bonus.
  • The Age of Revolutions splendor ability ‘Napoleonic Warfare’ gives a further +3 Artillery bonus vs fort. (Requires Mandate of Heaven)
  • The bonus is equal to the total number of artillery regiments divided by (fort building level + 1), with a minimum of 2, as listed in the table below
  • A single regiment of artillery will always give at least a +1 bonus, regardless of fort level.
  • Each 1000 artillery soldiers count as 1 artillery. e.g. having 10 regiments with 100 artillery each is the same as 1 regiment with 1000.

Fort building level	+1	+2	+3	+4	+5	+6	+7	+8
Capital without fort	1	2	3	4	5	6	7	8
Castle (Fort level 2)	1	4	6	8	10	12	14	16
Bastion (Fort level 4)	1	6	9	12	15	18	21	24
Star fort (Fort level 6)	1	8	12	16	20	24	28	32
Fortress (Fort level 8)	1	10	15	20	25	30	35	40

• Blockade. If the province is coastal and not completely blockaded, a −2 penalty is applied, or −1 if the attacker is the rightful owner of the province. Partial blockades (anything less than 100% for the province in question) have no effect on sieges. Note that the blockading fleet doesn't have to be owned by the same nation as the sieging army, or even a part of the same war to help in a siege.
• Fort Level. The defender's Fort Level is applied as a penalty.
  • Obsolete Fort: If the attacker's technology allows the building of more advanced forts, they gain a bonus +1 per fort level difference to siegeing old forts. e. g. If attacker can build Star Forts (building level 3) and is sieging a Castle (building level 1), they gain a +2 bonus to dice rolls.
  • Insufficient Garrison: Having less than half of the maximum garrison gives the attacker a +1 bonus. If the fort has no garrison whatsoever (i.e., if the fort has been mothballed during this month), then the province is treated as unfortified and the siege will automatically succeed.
• Walls Breached. Each time the walls are breached, the breach status value will increase by 1, to a maximum of +3. If this value is at least +1, then the fort can also be assaulted (see below).

The highest possible starting bonus is +17: a capital fort (−1), obsolete by 3 fort levels (+3), with an insufficient garrison (+1), with a 6-siege general (+6) and at least 8 regiments of artillery (+8). The worst possible starting bonus is −11, for a level 8 fort in a capital (−9) with no blockade (−2).

Effects

The die roll may result in an increase of the siege status, which improves the results of future siege stages. Maximum siege status values goes up with the attacker's maximum fort building level. (12/13/14/15 for fort building level 1/2/3/4). Maximum breach status is always 3.

• If the unmodified roll is 1, a Disease Outbreak happens—the attacking army loses 5% of its troops, and the siege does not progress (a surrender takes priority over a Disease Outbreak).
• If a breach occurs, ignore all results on the table below except for "Surrender". If the fort does not surrender, add 1 to the breach status and 2 to the siege status. A breach occurs if:

  ${\text{unmodified roll}}+{\frac {{\text{Artillery bonus}}+{\text{Obsolete Fort bonus}}}{3}}+{\frac {\text{Attacker's maximum fort building level}}{10}}\geqslant 14$

  Or an artillery barrage is used (see below)

• Then look up the modified die roll on the table below.

Roll	Result	Effect	Garrison losses
4 or less	Status Quo	–	–
5 – 11	Supplies Shortage	+1 siege status	−1% garrison
12 – 13	Food Shortage	+2 siege status	−3% garrison
14 – 15	Water Shortage	+3 siege status	−5% garrison
16 – 19	Defenders Desert	+2 siege status	−10% garrison
20 or more	Surrender	Siege successful	–

The attacker needs at least a net +6 bonus to have a chance of ending the siege.

Artillery barrage

The option to conduct an artillery barrage becomes available when a siege has at least one full artillery regiment per fort level. This costs 50 military power and creates 3 breaches in the walls. In total, these add +3 permanent siege status. Rolling a natural breach is still possible and will affect the siege status but will not add another breach.

Naval barrage

Same as artillery barrage, but only available if the number of canons on ships adjacent to the fort divided by 100 equals the fort level.

Assault

The attacker may choose to assault the garrison with their infantry if the walls have been breached at least once. This can result in a speedy conclusion of the siege at the cost of 5 military power, and usually costs lots of lives. The attacker loses roughly 5 times as many troops as defender do and assaults on fully-manned forts are highly discouraged. Only infantry can assault. If all infantry units of the attacker are killed before the defenders are defeated, the remaining cavalry and artillery will continue the siege normally. Only $({\text{fort level}}\times 5000)$ men can be part of an assault per day.

Mechanics of an army

Main article: Army

Exile

An exiled army can be identified by a black flag attached to its unit icon. It can't fight, siege provinces or explore, and it won't lift fog of war even in the province it's in. However, it can traverse any territory (other than wasteland) without needing military access. It still suffers attrition and its regiments can still move between armies, though regiments can't be mixed between exiled and non-exiled armies.

An army will become exiled under the following circumstances:

• When a war ends, any army still in territory it doesn't have peacetime access to is exiled. This prevents it from being permanently stuck in a place it can't get out of, as well as preventing several exploits.
• When a war begins, any army in a neutral or hostile province that it only had access to through a military access agreement is exiled. This prevents troops from being placed outside their country's territory in preparation for war. An army in uncolonized land or the territory of a subject or ally won't be exiled, even if the ally isn't called into the war.
• When a native tribe migrates, any armies that happen to be in the province it migrated to at the time and don't otherwise have access are exiled.

It will stop being exiled when it either:

• enters a province that the army's country or one of their subjects control or own
  • This includes home provinces occupied by an enemy
• boards a transport ship that moves into a sea zone or is currently in one.

If an army is in combat when it gets exiled, the battle will end only if all of its enemies are no longer hostile. For example, if an army is fighting rebels in enemy territory when peace is signed, they will continue fighting despite being exiled.

Looting

Every province has a loot bar. This is the amount of gold available to be looted in the province and is determined by its development level: a province will gain 1 gold for every increase of 1 development level. The player can loot provinces they occupy or those which they are sieging, but troops must be present to do so. The amount of loot taken depends on the number and type of troops in the province. A full strength infantry/cavalry/artillery regiment loots 0.1/0.3/0.05 ducats per months. When a province's loot bar is empty no more loot can be taken from that province. A province will only begin to recover two years after the last successful looting, at a rate of 10% each month.

Looting is the main cause of devastation, which greatly reduces the owner's production income and manpower, as well as decreasing movement speed, supply limits and institution spread. Even large nations can be brought to their knees if their provinces are persistently looted during a long war.

Various ideas increase looting speed; this bonus increases the amount of ducats looted each month by the stated amount (and thus decreases the time taken to fully loot a province).

	Traditions	Ideas	Bonuses	Policies
+25%	Ashanti traditions Baluch traditions Cossack traditions Interlacustrine traditions Manipur traditions Zaporozhian traditions	Crimean idea 3: Lead Raids into Ruthenia Gelre idea 6: Loot as Payment Piratical idea 2: Plunder!	—	—
+20%	West African traditions	—	—	—
+10%	—	Anatolian idea 3: Akîncî Cavalry Berber idea 5: Tuareg Cavalry Chickasaw idea 5: Slave Raids Shan idea 5: Raiders	—	—

• +50% Assimilating Great Lakes culture group as Mughals

Attach to army

This action attaches the player's army to a friendly army, causing their army to travel and fight alongside the friendly unit without further input from the player. The army can be detached at any time except in battle. An attached army cannot board transports. Attaching units to an AI army will change its behavior, making it bolder and more willing to actively engage enemies.

Attack natives

See also: Colonization#Natives

The native population of a colony or uncolonized province can be eliminated using the attack natives military action. A native army equal in size to the local native population (rounded to the nearest thousand) will spawn immediately and must be defeated in battle to clear out the native population. This action costs military power proportional to the native population, aggressiveness, and ferocity, and will permanently reduce the potential value of the province from the native assimilation bonus. The elimination of all natives in a province will prevent any future raids on the local colony or any passing armies.

Scorched earth

An army in an owned and controlled province may scorch the earth for 5 military power, as long as it has not already been scorched. This increases devastation in the province by 5 and gives the province modifier “Scorched Earth”, lasting for 60 months with the following effects:

−50%

Local hostile movement speed

The devastation itself has the following effects (scaled to these figures at 100 devastation), decaying as devastation decays as usual:

	−100%	Local goods produced modifier
	−50%	Supply limit modifier
	−100%	Institution spread
	+10%	Local development cost
	−100%	Manpower modifier
	−100%	Sailors modifier
	−25%	Local hostile movement speed
	−25%	Local friendly movement speed

Scorching the earth can be useful when the player's army is too weak military to fend off attackers and their provinces are likely to be occupied. It increases attrition (hurting the enemy's manpower), and makes the provinces less valuable to the attacker while they're occupying them. The player will lose income in the meantime, but if they were going to lose control of them anyway it could be a good idea to make them less valuable for the enemy.

Automatic Rebel Suppression

Clicking the Automatic Rebel Suppression icon in a selected army panel will set the army to automatically travel to and fight rebel armies that appear in its surroundings. The army will return to its previous position after the rebels are dispatched. Armies that are ordered to move will stop suppressing rebels.

Units set to auto suppression reduce unrest by a greater amount than normal.

Forced march

Forced march makes an army move 50% faster, but costs 1 military power for each province the army marches through. Forced march is available at administrative technology 15. Armies that are forced marching do not recover morale. During Age of Revolutions it is possible to enable Improved Force March ability, which reduces military power cost to 0 (requires Mandate of Heaven).

References

Warfare