Subject nations are semi-independent subordinate nations that surrender their economic, diplomatic and/or military power to another country in exchange for protection by their overlord. It is possible to see a subject's nation information by selecting the country icon on the subjects tab. The types of subject nations range from the primarily economic Trade company to the military-focused March. All subjects (except trade companies) have a liberty desire that determines their loyalty towards their liege.
- Main article: Vassal
Vassals are the most basic form of subject nations. They are required to pay a portion of their tax income to their overlord but do not transfer trade power to their overlord like other particular subject types(vassals of a merchant republic transfer 50% of their trade power to their overlord if Wealth of Nations is active). While vassals may have control over their own territory and military, they also automatically join any conflict their overlord enters into.
Vassalization can occur militarily by forcing it upon a defeated enemy in a war. Diplomatic vassalage can occur if a military alliance exists and relations are high (above 190). Vassals cannot declare war, but can fabricate claims that either they or their overlord deems as 'Vital Interest'. Vassals with over 50% liberty desire can request a support of independence from other nations, and break free through an independence war. Vassals with over 50% liberty desire are also more active diplomatically as to forming their own alliances with other rebellious subjects of their overlord and setting more provinces as those of interest.
After a nation has been a vassal of another country for at least ten years, their overlord can begin diplomatically integrating them into the overlord's domain. This results in the vassal's annexation.
|Available only with the Art of War DLC enabled.|
- Main article: March
March status can be revoked and the subject turned into a simple vassal but at the cost of stability and relations loss.
|Available only with the Art of War DLC enabled.|
- Main article: Client state
Generally, any province within two tiles by land can be added to a client state, including over straits. The first province that a new client state is given is automatically designated as the capital, and the culture in that province will become the primary culture of the new client state. The client state will have its creator's state religion.
It is possible to customize the flag, the name and the map colour of a client state based on a set of flag templates and images. With Common Sense, this can be done at any time after it's created. However, if you make a client state into a march, customization (such as flag, name, map color) won't be available until you convert it back to vassalization.
- Main article: Personal union
Junior partners in a personal union share the same ruler as that of the leading country. Like vassals, junior partners of a personal union will automatically go to war if their overlord does, but they do not have to provide their overlord with a percentage of their monthly income, and only get a small +10 relations boost with their overlord. The junior retains any subjects it had, except other unions, which the overlord inherits.
Personal unions can occur when a ruler dies without a legal heir. In this case, if a royal marriage partner shares the same dynasty as the deceased ruler, it becomes the senior partner in a union. A succession war may erupt between rivals or valid partners. Additionally, a claim throne casus belli can be used on nations with a disputed succession (weak or no heir) of the same dynasty that the player has a royal marriage with.
Personal union partners can be inherited or integrated provided the union has been stable for fifty years. Diplomatic integration annexes the junior partner at the cost of diplomatic monarch points. Inheritance automatically annexes the junior partner with no autonomy, but occurs only upon ruler death. The probability of inheritance increases with the senior partner's diplomatic reputation and stability and decreases with the junior partner's number of provinces.
A personal union can end upon the death of the senior ruler when the junior partner has a negative opinion of its senior. If this occurs, the former senior partner will get a "Restoration of Union" casus belli on the former junior partner, allowing the union to be reinstated militarily.
Some nations can get a "Restoration of Union" CB against countries that they never had a union with in the first place, such as Austria, which can receive this casus belli against Bohemia and Hungary as a mission.
Only nations that have one of the Christian denominations as their state religion are able to form personal unions.
- Main article: Colonial nation
Colonial nations represent the distant New World colonial territories of European powers. They will automatically form once five cored colonial provinces exist inside a single colonial region. Once formed, colonial nations will take control of any province that would otherwise be owned by their overlord in a given colonial region, even if the province is uncored or would otherwise cause extreme overextension.
When created, the colonial nation's flag is generated based on the mother country's flag and the colonial region the new Colonial Nation is located in. For example, a nation in the Mexico colonial region will have a yellow flag, while one in the Eastern North America colonial region will have a light-blue one. With Common Sense, the name can be changed after creation (but unlike client states, nothing else can be customized).
|Available only with the Wealth of Nations DLC enabled.|
- Main article: Trade company
A province in a trade company provides approximately half the income, no manpower, and no sailors to the home country but produces double the trade power and adds 0.5 naval force limit. Additionally, goods produced remains unaffected by cultural intolerance, religious intolerance is ignored, and the province does not contribute to religious unity.
Trade companies may be formed by nations that own at least one province in any of the 15 trade company regions scattered throughout Africa and Asia. As of version 1.30, this restriction no longer applies, and any province in a territory which is on a different subcontinent from one's capital and not in a colonial region is eligible to become a trade company. They differ from colonial nations in the Americas and Australia in that they are not separate governments, as all territories remain part of the mother country. Provinces in trade company must belong to a territory - adding them to a state will automatically remove them from a trade company, which entails the same -200% goods produced modifier which manually removing one does. Provinces can be added or removed from a trade company at any time, except when the 5-year goods produced modifier for removal is present.
Please help with verifying or updating this section. It was last verified for version 1.27.
|Available only with the Mandate of Heaven DLC enabled.|
Tributaries are a loose form of subject relationship available to nations in the Eastern religion group, as well as to steppe hordes and the Emperor of China regardless of religion. They do not occupy relation slot. Tributaries retain full diplomatic independence and may start wars and have subjects of their own. The overlord receives a call to arms if the tributary is attacked (unless if by another tributary of the same overlord), but does not have to accept. Each year, the overlord may demand a tribute of money, manpower, or any of the 3 types of monarch points. The tribute is paid annually on January 2. Tribute type demand must be selected before January 1. The default tribute is money. If the tributary pays the tribute, trust increases slightly; if it refuses, trust falls significantly. AI always pays tribute when Liberty Desire is below 50% and refuses otherwise.
Monetary tribute is 12.5% of annual income, manpower tribute is 25% of annual gain, and monarch point tribute is 1 per 33 developments (rounded down) and capped at 12 for 400 or more development. If monetary tribute would be below 1 ducat, or monarch point would be below 1 point, they can't be selected. 
Either party may renounce the tributary status at will, unless they have a truce. The overlord gets a one-way five-year truce with the former tributary, but the former tributary may attack the overlord immediately. Tributaries who renounce their status lose -1 stability; this can be circumvented by refusing tribute until the overlord breaks the agreement on their own.
|Attitude towards proposer||Hostile: -1000|
|Opinion towards proposer||+1 per 4 positive points (rounded down)|
|-1 per 4 negative points (rounded up)|
|Proposer's diplomatic reputation||+2 per positive point|
|-2 per negative point|
|AI nation's government rank||-20/-100 Kingdom/Empire|
|AI nation's development||-0.5 per development (rounded up)|
|Proposer economic base compared to target nation||+90 to -90|
|Proposer military power compared to target nation||+90 to -90|
|AI nation has subject of its own||-1000|
|Are not neighbors||-1000|
|Distance between borders||-0.5 per distance between borders (defunct but still displayed)|
|Proposer is Celestial Empire or has horde government with rank Empire||+10|
For a tributary overlord, sending manpower to tributary subjects at war can often be the cheapest way to decrease liberty desire and maintain the more value tribute income in the form of monarch powers. It can thus be helpful to set large tributary countries as "special interest" (right-click on country flag in provincial interface) and receive notification for wars by these tributaries.
For establishing tributary subject of AI nation, threatened attitude gives the most significant +100. (Strangely, friendly attitude does not give any modifier.) The attitude goes away at high opinion. Thus the optimal opinion with the threatened attitude is around 0. Player should avoid improving relation for too long in that case.
- Main article: Japan#Daimyo & Shogunate
Daimyo are a unique form of vassal for the shogun of Japan. They may ally with and fight other daimyo, but not foreign countries. They do not occupy a relation slot, and the shogun has several special vassal interactions for them. Note: outside nations can enforce peace on two warring daimyos without calling the shogun or its vassals to war, effectively providing a way for outside powers to get easy land on japan.
In previous versions of the game, technologically backward nations could be made protectorates, which exchanged a transfer of trade power and not being allowed other allies for protection from hostile nations and a discount on technology cost. They did not occupy a diplomatic relations slot. Protectorates were merged with regular vassals in patch 1.20.
Please help with verifying or updating this section. It was last verified for version 1.25.
All subject nations have a liberty desire between 0 and 100, indicating their wish for independence.
- Below 50 a subject state is loyal: it pays taxes/tariffs to its overlord and takes an active part in all wars.
- Above 50 liberty desire, a subject becomes disloyal, refusing to pay taxes while being unhelpful in wars by only defending its own territory. Disloyal subjects readily accept support for their independence from foreign nations and make alliances with each other, and may declare an independence war if they have sufficient strength. In rare cases, a disloyal subject may still have a Friendly attitude toward its overlord; this means it will not accept requests to support its independence or alliances from fellow subjects, but does not otherwise alter its behavior.
- At 100 liberty desire, a state is rebellious, and will, at least in theory, declare its independence at the slightest opportunity.
Liberty desire depends on the sum of the following factors:
- The relative army size of the subject compared to its overlord. There is +75 liberty desire for having 100% of the overlord's forces, scaling proportionately (e.g. +37.5 at 50%).
- The combined strength of all vassals, marches, and client states is used for their liberty desire.
- Personal union partners, daimyos, and colonial nations only consider their individual strengths.
- Additionally, nations allied with or supporting the liberty of a subject nation will have their army strength added to that specific subject. Other subjects will not have their army strength increased, unless their independence is also supported.
- A base modifier depending on type of subject: −25 for client states, −15 for marches, +10 for Japanese daimyo; 0 for vassals, colonies and personal union partners.
- +0.25 per point of development for vassals, client states, and marches.
- +5 for each level the overlord's diplomatic technology is behind the subject's.
- −0.1 for each point of positive relations (max −20), +0.2 for each point of negative relations (max +40).
- −5 for a royal marriage.
- −50 for historical friends.
- +50 for historical rivals.
- +10 subject nation is a Steppe nomads.
- −3 per point of diplomatic reputation.
- ±0.4 per point of trust below/above 50 (min −20 at 100 trust, max +20 at 0 trust)
- +1 per point of the overlord's war exhaustion for colonial nations.
- −50 if recently defeated in an independence war (decreasing over time).
- +0.2 for colonies, per point of the colonial nation's administrative efficiency.
- +1 for colonies, per point of tariff rate.
- −0.5 per granted province development (sum decreasing over time by 0.1 per month).
- −5 per each development point improved in subject's province (sum decreasing over time by 1 per year).
- +1 per each prestige below 0 (-50 prestige equals +50 liberty desire)
Certain ideas reduce liberty desire in subjects:
Subject interactions 
All subject nations are listed in the subjects tab in country interface.
- Subject interactions require Common Sense DLC unless another DLC (or none) is indicated.
- Since tributaries don't exist without Mandate of Heaven DLC, that is also needed for them.
- Client states are special kinds of vassal or march and so have most of the same interactions.
- Daimyo also have most of the same interactions as vassals; those that are different are noted, and their unique interactions also require Mandate of Heaven DLC.
- Liberty Desire modifiers from most sources, such as events and province defections, decay at ±0.1% per month. Toggled liberty desire modifiers (embargo rivals, support royalists, subsidize armies, divert trade, send officers) last until cancelled. Liberty desire from tariffs is permanent.
|Block/Allow Settlement Growth||Subject cannot start using a colonist to promote settlement growth. Using Allow Settlement Growth allows it again.||Does not stop any existing colonist mission. Doesn't prevent the colonization of uncolonized provinces.|
|Contribute to Capital||Subject's province with the highest development loses 2 development of its best category (biased towards tax and then production). The overlord's capital gains 1 of the same type.|
|Customize Subject||Subject is a client state or colonial nation||Change the subject's name and/or (for client states) its map colour and coat of arms.|
|Demand Additional Tribute||Liberty desire less than 50%|
|Embargo Rivals||Has at least one rival|
|Enforce Culture||Liberty desire less than 50%|
|Enforce Religion||Decays by 1% per year (around 0.1% each month)|
|Fortify March||Fort is built, paid for by the overlord|
|Grant Core/Claim||Core/claim is granted to the subject||A permanent claim granted will still be permanent.|
|Pay Off Debt||
|Placate Local Rulers||Has positive prestige|
|Place Relative on Throne||
|Replace Governor||Choice between 4/2/2, 2/4/2 or 2/2/4. Does not affect the colony's republican tradition.|
|Seize Land||Cannot seize capital|
|Send Additional Troops||Subject is at war|
|Siphon Income||Subject has positive opinion of overlord|
|Start War in Colony||
||This only works against colonial nations and primitive countries. It can't be used against countries which reformed their religion/government.|
Trade companies have no subject interactions per se, but they do have one toggle button in the subjects tab:
- Promote Investments: +50% Trade power in all provinces owned by the trade company, +0.03% yearly inflation
Enhance provinces of subject nations
|Available only with the Rights of Man DLC enabled.|
It is possible for the overlord to construct buildings in the provinces of subjects, and to develop them. Each time the overlord develops a subject's province, their liberty desire is reduced by 5%, decaying by +0.1% per month. However, since this increases the subject's development, it also increases base liberty desire by +0.25 for those subject types that have development-based liberty desire (i.e. not personal unions), and can increase their liberty desire based on relative power.
|Available only with the Art of War DLC enabled.|
A nation can set its subject's military focus to any of the following, which will determine how they behave in wars. If the subject has more than 50% liberty desire, they will always behave as though set to passive.
|No focus||The subject will decide its own strategies.|
|Supportive||The subject will seek to attach to friendly armies.|
|Aggressive||The subject will be aggressive towards enemies, seeking battles in enemy territory.|
|Available only with the Rights of Man DLC enabled.|
|Passive||This will make the subject stay with armies in their own territory, and defend there. Unless escaping a larger threat.|
|Defensive||This will make the subject defend its allies' territory. (Recommended for stronger subjects)|
|Siege||This will make the subject use its armies to siege down hostile fortresses and not seek any battles.|
- See in TRIBUTE_BASE_. : variables with
- See in DIPLOMATIC_ACTION_TRIBUTARY_ACCEPTANCE_PER_DEVELOPMENT. :
- See in DIPLOMATIC_ACTION_TRIBUTARY_EMPIRE_FACTOR. :