User:General Baker/Sandbox/Diplomacy

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Diplomacy in EU4 operates using a 'bilateral system'. For example, the player country may have positive relations with another country whilst that country might have negative relations with the player. Relations can be increased by having alliances, being in the same coalition, fighting a common war, having a common rival, decisions, events and placing a diplomat in their capital. Relations are decreased by declaring war on them, being rivals, sending insults, having a different religion, breaking/dishonouring an alliance, events and decisions.

Reasons for a nation liking/hating you will be displayed and will be capped at +200. If your diplomat is removed from a foreign nation's capital the bonus will change by -3 a year.

Diplomacy is conducted by diplomats, and the diplomatic options available to diplomats depends on a countries technology and ideas. Diplomatic options are split in seven categories: Alliance, Influence, Relations, Dynastic, Covert, Economy and Access actions. The declare war and sue for peace diplomatic options are found outside of the categories.


A Diplomat is required to perform most diplomatic actions. Some actions - improving relations, annexing a vassal, and all covert activities - will tie up a diplomat until the task is completed, although they may be recalled home earlier. Other actions are immediate. After completing a mission, a diplomat will be unavailable while he travels back home, which can take anywhere from a few days if returning from a neighbor to a year if on the opposite side of the globe.

Gaining diplomats

Each country starts with 2 diplomats by default, but more can be gained throughout the game:

Diplomatic reputation.pngDiplomatic reputation

A nation's diplomatic reputation represents its overall diplomatic ability and credibility; it replaces the diplomatic skill of EU3. Diplomatic reputation is visible in the diplomacy window for one's own country.


Each point of reputation gives:

  • Reasons for other countries to accept diplomatic proposals:
Action Reasons
Offer Alliance 3
Royal Marriage 4
Offer Vassalization 1
Ask for Military Access 2
Ask for Fleet Basing Rights 2
  • +2% chance to inherit lesser partner in a Personal Union.
  • +0.1% progress per month during diplomatic annexation or integration.

Gaining diplomatic reputation

  • Legitimacy: -2.5 to +2.5.
  • Overextension: -2 per 100%.
  • Being in the HRE: 2.
  • Trading in Ivory: 2.
  • Diplomatic Influence (Diplomatic Ideas): 3.
  • Experienced Diplomats (Expansion Ideas): 3.
  • Statesman advisor: 5.
  • Judiciary Act: 1.

Diplomatic relations.pngDiplomatic relations cap

A nation may only form diplomatic agreements with a limited number of other nations before overtaxing its diplomatic corps. Each relation over the cap costs 1 diplomatic monarch point per month. The limit is on the number of countries, not the number of deals, so having multiple agreements with a single nation only counts once.

Agreements that count towards the cap include:

  • Alliances
  • Royal Marriages
  • Guarantees
  • Having a vassal or junior PU partner.
  • Getting military access

Agreements that do NOT count toward the cap include:

  • Giving military access.
  • Getting or giving fleet basing rights.
  • Getting or giving loans.
  • Coalitions
  • Embargoes
  • Warnings
  • War subsidies

Increasing the diplomatic relations cap

The base is 4 diplomatic relations.

  • Cabinet (Diplomatic Ideas) and Additional Diplomats (Expansion Ideas) give +2 each.
  • The Palatinate has an idea giving +1 relation.
  • Austria, France, England, Ethiopia, Savoy, Saxony and the Berber states have ideas giving +2 relations.
  • The Holy Roman Emperor gets +2 relations.
  • The Shogun of Japan gets +4 relations.
  • Certain events give a temporary increase in the relations cap.
  • The AI gets +1 relation. It will rarely use this relation, so the player is usually able to propose an agreement with an AI nation without running into the AI's cap.


See also: Warfare

Declare war

This will declare war on the target country. See Warfare for more information on wars.

Casus Belli

A Reason for War, each Casus Belli represents a valid reason for one country to declare war on another. A Casus Belli is required to avoid a stability drop when Declaring War. Valid Casus Bellis include:

  • Reconquest (Take some land where you have a core on)
  • Conquest (Take some land where you have a claim on)
  • Dishonorable Scum (They have been too expansionist and are considered scum by the world entire. This is one of the best CBs because you can do basically everything with reduced aggressive expansion)
  • Claim Throne (You have the chance to force a Personal Union if their Heir has a Weak claim or there is no heir, provided you have a Royal Marriage)
  • Show Superiority (They have Insulted you)
  • Trade Disputes (They have Embargoed you, or you are a Merchant Republic and going to declare war to another Merchant Republic w/o any other CB)
  • Colonialism (Take your enemy's colonies near yours)

Sue for peace

Main article: Ending a war

Will open the peace negotiation screen where you will negotiate your demands, the terms of your surrender or simply a white peace. Remember, when fighting against a coalition, you may only sue the leader of the coalition, unlike an alliance, where you may sue the lesser parties individually, then the leader to close the deal for maximum profit.

Call to arms

Ask an ally to join a war. Does not require a diplomat to use.

Alliance actions

Main article: Alliances

Offer alliance

Will allow you and your alliance partners to call each other to wars. A Casus Belli is given against an Alliance Partner's enemies if one was not called to the war.

Dissolve alliance

Dissolves an alliance with the target country if one exists.

Form coalition

Sometimes you simply do not want to ally with someone because they are likely to drag you into a bunch of wars that you have no interest in, but, at the same time you think they would make a great ally for the war you do want to wage.

EUIV addresses this problem with the coalition system, a mutual alliance that is directed against a single country. You have an alliance leader, say the Papacy, who organizes an alliance say directed against Venice. Then they sign up countries like France, Milan and Austria. The alliance only fires in the event of war with Venice but if war does erupt all countries in the Coalition will be called in.

Initially, this power is only open to Catholic countries and can only be organized by the Papal Controller, reinforcing the idea that the Pope is still quite important in the early centuries of the game. Later on though, advances in diplomatic technology will allow any country to organize its own coalition against a common rival. Some Dynamic Historical Events can form some historic coalitions if the stars are aligned properly, as well.

Coalitions become, then, a great way to contain a growing threat or hated neighbor since everyone signs on to fight before the war starts. It can be challenging to get a coalition moving, since you need your potential allies to see the strategic threats in the same way you do. But it is a valuable tool that reinforces common interests.

Influence actions

Enforce peace

Demand that a country make peace in a war - refusal will bring you in to the war on the side of the defender. You can't enforce peace on a defender and you need to have at least 100 relations with the nation you want to protect.

Proclaim guarantee

Will call you into the war if someone declares war on the guaranteed country.

Relations actions

See also: Relations

Improve relations

This sends one of your diplomats to the target country and will improve relations over time. Relations can be improved up to +100 modifier for independent realms, and up to +200 for dependent states (vassals, lesser partners in personal unions). Improved relations decay by -3/year (base value) if there's no diplomat currently improving relations with the target country.

Send warning

This will give you a call to arms if the target country attacks one of your neighbors. Country A cannot warn Country B if B has already warned A.

Send an insult

This will give the target country a casus belli on you for one year and lower relations with -25.

Dynastic actions

Royal marriage

For the dynastic effects of Royal Marriage, see Ruler#Royal marriage

Countries ruled by monarchs may arrange royal marriages with others. This will improve relations permanently by +25 whilst in effect. Attacking a country with which royal ties are established results in a stability drop. The ties can be severed at the cost of stability drop and deteriorated relations with the target country, however the Papal controller can invoke divine dispensation and forego the reduced stability.

Royal marriages are unavailable to republics (with the exception of Noble Republics), theocracies, and with countries of a different religion group.

Offer vassalization

Main article: vassal

Will peacefully vassalise the target country.


  1. The player must have 190 relations with the target country.
  2. The player must have a royal marriage and alliance with the target country.
  3. The target country cannot be at war.
  4. Both nations must be in the same religious group.
  5. The target is willing to accept vassalization (see the vassal page for details)

Annex vassal

The diplomat will begin peacefully annexing the vassal.


  1. Has been a vassal for at least 10 years.
  2. Relations of at least 190.


When target country is minor partner in a Personal Union, this will integrate it.


  1. Has been partner for at least 50 years.
  2. Relations of at least 190.

The time to integrate a vassal or union partner depends on diplomatic reputation, the time the nation has been a vassal and the level of war exhaustion and overextension.

Claim throne


Casus belli
Will give you a casus belli to create a personal union with the target country. Will form Personal Union if ruler of target country dies without an heir. If more than one country claimed a throne, a succession war will follow.

Covert actions

See also: Espionage

Fabricate claims

A diplomat can be sent to another neighbouring nation to fabricate a claim on a neighbour province, this includes province that share a sea zone. Fabricating a claim can take up to three years or longer, and each time a diplomat gets discovered, the progress of the claim drops by 10%. Once a claim is "established", the fabricating country now has a legal reason to start a war – a casus belli. Claims last 25 years, and will stay until the time is up or the province has become a core. Peace deals do not affect a claim. Claims allow a nation to select the targeted province as a wargoal. Provinces with a claim cost less warscore in peace deals and are 25% cheaper to core.

Support rebels

Main article: Rebellion#Support rebels

A diplomat can always be sent to another neighbouring nation to support a rebellion.

Infiltrate administration

If a nation wants to infiltrate the administration of another country they will need to have the 'Espionage' spy idea to take this covert action. So long as a diplomat is present in the enemy capital, the fog of war is lifted over their country, revealing everything within their territory. As soon as the diplomat is discovered, he is sent home and the fog is returned.

Sow discontent

If a nation wants to sow discontent in another country they will need to have the 'Destabilizing Efforts' spy idea to take this covert action. So long as a diplomat is present in the enemy capital, the target country gets more expensive stability costs, and a higher chance of revolt. A country can only be targeted by either one Sow Discontent at once.

Sabotage reputation

If a nation wants to sabotage the reputation of another country they will need to have the 'Rumourmongering' idea, the third available in the Espionage idea group. So long as a diplomat is present in the enemy country, all neighbours, enemies and rivals of the targeted country gets an opinion penalty towards the target. This will make it more difficult for the target to recover its reputation from recent expansions or betrayals, to make alliances and to enter other diplomatic agreements. A country can only have one sabotage on them at the same time.

Economy actions

See also: Economy

Issue embargo

Reduces the trade power of the target country in any trade node you have power in, depending on several factors.

Send gift

Allows you to send money to improve relations with a country, up to a maximum of +25. The base cost is 25 ducats, but larger nations will require more money to get the full relations boost. The bonus lasts for 5 years. Multiple gifts do not stack.

Loan offer

Allows you to loan out money to other countries for interest. When the loan is due to be repaid, the loan-taker can instead choose to keep the ducats. This will give the loan-giver a casus-belli.

War subsides

Gives a specified amount of money to a country if they are at war.

Sell province

Sell a province for money. You may only sell one province at a time. The AI will never buy a province that it cannot core (due to distance or lack of a border), buy a non-core HRE province, or buy any non-core if it has high overextension. The AI will sometimes offer to sell isolated and indefensible provinces to the player.

Access actions

Military access

Allows you or the target country to pass through each other's territories. Reputation is increased by 10 until the military access is revoked by either country.

Fleet basing rights

Allows you or the target country to base fleets in each other's ports, which lets the benefiting nation repair ships and increase the naval range for repairing and colonizing. Note that this diplomatic action costs 0.2 ducats each month for each port in the nation giving rights.


These actions are not in the main list, but are also conducted via the Diplomacy panel.

Select rival

Selecting a rival costs 10 Diplomatic power. Up to three countries may be selected as rivals at any time. Doing so has the following effects:

  • The country is an enemy of their rivals, with its attendant effects on diplomacy.
  • +25% prestige from defeating a rival in battle.
  • No Trade Efficiency penalty from embargoing the rival.
  • +20% spy offense against the rival.
  • -33% Diplomatic Power cost for demanding provinces from the rival in peace deals.

Create vassal

This releases a country as a vassal. The released country gets all of their core provinces that are owned by the releasing country, except for the releasing country's capital if applicable.

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