Personal union

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Personal union.png
personal union is a form of diplomatic relationship where one monarch rules over two nations. It can be formed by having a royal marriage with a country whose monarch dies without an heir (usually of the same dynasty). It may also be formed by enforcing a claim through war or, in certain nations, through an event or decision. Once formed, it works similar to vassalage: the nation leading the union (the senior partner) gains the throne and puppets the nation who lost their monarch (the junior partner). Personal unions can only be formed between Christian monarchies (Catholic, Protestant, Reformed, Orthodox and Coptic).

Unlike other subject types, the junior partner in a personal union can have their own subjects. For example, forcing a union over Bohemia as Austria will not end their overlordship over their vassal Silesia.

Countries starting with a personal union in 1444[edit]

Forming a personal union[edit]

There are several ways in which a player can form a personal union, or fall subject to one.

Personal union by event[edit]

Several countries in this game have the opportunity to form a Personal Union with another country through an event. All events resulting in a Personal Union can only fire if the junior partner is AI controlled (e.g. if the player chooses Aragon, the Iberian Wedding event will not fire).

  • Poland can form a Personal Union over Lithuania through its Successor of Wladyslaw III event. This will result in Lithuania forming a Personal Union under Poland, and later enables the Polish decision to Form the Polish-Lithuanian Commonwealth.
  • Castile can form a Personal Union over Aragon through its Iberian Wedding event. This will also make Castile the senior partner in a Personal Union over Naples, if they are in a Personal Union under Aragon at the time that the event fires. This enables Castile to later Form the Spanish Nation Diplomatically.
  • Aragon can also form a Personal Union over Castile through the Aragonese Iberian Wedding Event if Aragon is controlled by a player. Aragon can later take a decision to inherit Castile and form Spain.
  • Naples can receive an event that allows it to be in a Personal Union under France.
  • Any Christian country can get an event that can lead to a peaceful union with another Christian nation if both rulers are between 16 and 40 and the two nations involved neighbor each other, have a high enough opinion of each other, have no heirs, both rulers are of a different sex and are either of the same dynasty or in the same culture group. This event is quite rare (MTTH is 500 months).
  • Brandenburg can get a personal union over Prussia if Prussia is a vassal of Brandenburg or if Prussia's opinion of Brandenburg is at least +100. (This event can still fire even if Prussia is a vassal of another country).
  • Brandenburg can form a union over Ansbach if their initial 1444 heir Albrecht Achilles ascends the throne while the 1444 Ansbach monarch Albrecht Achilles II still reigns. (They are the same person)

Personal union through diplomatic means[edit]

For two countries to form a Personal Union diplomatically the following prerequisites need to be met:

  • The potential senior partner either
    • has a royal marriage with the target country (potential junior partner), or
    • has claimed the throne of the target country
  • The target country has no heir
  • The target country is not already a senior partner in a Personal Union
  • The target country is at peace

Chances are additionally improved if the two countries share a dynasty.

Forming a personal union is not technically restricted to kingdoms - Republics (notably noble republics and the Dutch republic) can also become the senior partner (but not the junior partner) in a personal union if all conditions are met. The player can check at any time if a target country is at danger of falling under a personal union by hovering over that country's king's name in the diplomatic view and checking the text after "On Monarch Death:". Countries that have no heir are listed in the "Disputed Succession" alert with a yellow font; such countries with the player's dynasty or a royal marriage are listed in green font. The player will receive a red alert themselves if they are in danger of becoming the junior partner in a personal union.

If the ruler of the target country then dies heirless, the target country is at peace, and there are countries that can become a potential senior partner to the target country, the country with the highest development (taking into account local autonomy) will then be chosen to lead a personal union over the target country. Take note that claiming a throne causes a -100 opinion malus with the target country, and a -50 opinion malus with all countries that the player has a royal marriage with.

When a country falls into a personal union under another country in such a manner, the game will identify another country among all countries that share the same dynasty, have rivaled the new senior partner, or have a royal marriage with either the new senior partner or the new junior partner. They will receive an event where they can either accept or decline to enter a succession war over the new junior partner. If no country is willing to contest the personal union, the target country will fall under a personal union of the new senior partner peacefully. If a succession war ensues, the attacker, if successful, can enforce a union over the junior partner, or demand that the senior partner release the target country.

The player, in order to maximize his chances of becoming the senior partner in a personal union, will need to get their dynasty on as many countries' thrones as possible. A target country can adopt the player's dynasty if the target country's king dies without an heir or the target country is in an Interregnum, the target country will not fall under a Personal Union when the king dies, the target country has a high opinion of the player, and the player has higher prestige than the target country. The chances increase if the player has more than 4 royal marriages. The player can check this at any time by hovering the target country's king's name; it says "a noble from X succeeds to the throne" if that is the case.

In order to further increase the chances of the player's dynasty spreading, they can target kingdoms with old rulers and no heirs specifically, ideally those that have few royal marriages. The player can check this at any time through the "disputed succession" alert.

Personal union through war[edit]

A country can form a Personal Union by attacking another country using either of two casus belli: Claim on Throne and Restoration of Union. The Claim on Throne CB can be acquired by taking the claim throne diplomatic action if the target country shares the same dynasty, has either no heir or an heir with a weak claim and has a royal marriage with the country. If the country has acquired the CB in this way, the claim will expire if the target country obtains an heir with a strong or average claim. (Note that dissolving an alliance will cause a 5-year truce.) England has the opportunity to gain this CB on France through the Occupy Paris mission.

The Restoration of Union CB is acquired by senior partners of a personal union if the junior partner breaks free (cf. #Ending a personal union). Austria can also also gain this CB on both Bohemia through the "Bohemia must accept Austrian overlordship" mission, and on Hungary through the "The decline of Hungary" mission. The Netherlands can gain this CB on England or Great Britain through the "Invitation to $MONARCH$" event.

In order to enforce the claim, the player needs to attack the target country using either of the two casus belli. While the target country is able to call in all its allies as this is a defensive war for them, some or all the player's allies may be unwilling to join due to the opinion modifier "does not want X in a personal union under Y". The war goal with either CB is to occupy the target country's capital, and enforcing the union costs 84% (claim throne) / 60% (restoration of union) war score, regardless of size. This will cause aggressive expansion relative to the target country's size. Enforcing the union will also cause a -100 opinion modifier with the new subject (which is on top of the potential -100 opinion modifier caused by claiming their throne).

Subject interaction[edit]

Main article: Subject_nation#Subject_interactions

As with all subjects, it is possible to interact with a junior partner. This is done through the subject interaction section of the subject tab of the country interface.


A personal union is similar to vassalage. The senior partner controls the diplomacy of the junior partner, the junior partner will always join their wars and will always occupy provinces for the senior partner, as long as their liberty desire doesn't rise above 50%. The junior partner cannot declare war, negotiate separate peace treaties or enter royal marriages. As in vassalage, being the senior partner of an elector in the Holy Roman Empire will result in a +50 point bonus to their electoral vote and a -50 point malus from all non controlled electors.

However, unlike a vassal, the player does not receive any income from lesser partners in a personal union.

Ending a personal union [edit]

A personal union can end in any of the following ways:

  • Incorporation of the junior partner into the senior partner, by integration or inheritance
  • The junior partner declaring independence and winning the war
  • The ruler dying while the junior partner has a negative opinion of the overlord
  • Pretender rebels enforcing their demands in the junior partner
  • Religious rebels enforcing demands that change the state religion to a heathen religion
  • Rebels enforcing demands that change government type
  • Peacefully abandoning a PU with a lesser partner at the cost of:
    • 25 Prestige
    • Truce of 5 years between the former overlord and the released country
    • Opinion penalty linearly scaling with liberty desire from -200 to 0 for 0% to 100% liberty desire, respectively.


After 50 years, the overlord nation can inherit their personal union subjects if the overlord has more provinces than the PU subject nation. Inheriting the PU subject can occur each time the ruler dies. This chance may be 0%; to see the probability, the player may hover over the king's name in the diplomacy screen. The main factors for inheritance chance are Diplomatic reputation.pngDiplomatic Reputation of the senior partner and the province count of the junior partner. The full probability can be calculated as 5 x Diplomatic Reputation (Senior) + Stability (Senior) + 5 if both partners share a culture group - 1 per province in the junior partner.

Note: Player-controlled nations will never be inherited on monarch death, though they may still be integrated manually by their overlord.


A junior partner in a personal union can be diplomatically integrated by the senior partner through the Integrate option. Integration occupies a Diplomat.pngdiplomat until complete, and results in direct control of the former junior partner's territory and military, while also gaining control of its subject nations.

The requirements for initiating integration of a junior partner in a personal union are:

  1. Union has been stable for at least 50 years.
  2. Junior partner's opinion of senior partner is at least 190.
  3. Liberty desire is less than 50%.
  4. Senior partner has more provinces than junior partner.
  5. Junior partner is at peace.
  6. Junior partner has control of its Capital.pngcapital.

Integration progress of junior partners appears in the diplomacy interface as a small vertical progress bar next to the personal union icon Personal union.png. If the integration process is cancelled before completion, all progress is lost, including the invested Diplomatic power.pngdiplomatic power. Unlike Vassal.pngvassal annexation, personal union integration can be cancelled if the personal union ends.

Integration will be paused if:

If the annexation process is cancelled before completion, all progress is lost, including the invested Diplomatic power.png diplomatic power. Diplomatic integration begins from 0 progress at this point.

The total cost of integration is 8 Diplomatic power.png diplomatic power per Development.png development of the junior partner. This cost is increased by the Hostile core-creation cost on us.pnghostile core-creation cost modifiers of the junior partner's corresponding provinces, and decreased by Administrative efficiency.pngadministrative efficiency and modifiers that reduce Diplomatic annexation costannexation cost. These modifiers are displayed below:

Diplomatic annexation cost Traditions Ideas Bonuses Policies
  • Influence idea 3: Integrated Elites
  • Influence-Administrative: Vassal Integration Act
  • Austrian idea 1: Imperial Ambition
  • Zambezi idea 6: Wealth of the Shire Valley
  • Naxian ambition
  • Plutocratic-Influence: Full Sovereignty Act

The full formula for diplomatic integration cost is:

\text{dip point cost} = \text{floor}\left( \sum_\text{per province}\left[ 8 \cdot \text{development} \cdot (1 - \text{administrative efficiency}) \cdot \left(1 + \sum\text{annexation cost modifiers}\right) \cdot \left(1 + \sum\text{local coring cost modifiers}\right) \right] \right)

The senior partner invests diplomatic power into the integration process each month at the following rate:

If the total is 0 or negative, integration will pause, but not reverse.

Completing diplomatic integration of a junior partner results in the following effects:

  • +5 prestige.
  • "Annexed Subjects" national modifier for 10 years giving -3 Diplomatic reputation.png diplomatic reputation.
  • -25 relations with other HRE members, if the junior partner was in the Holy Roman Empire.
  • Control of all the junior partner's provinces, army, and navy. This may put the senior partner over its force limit.
  • Control of the junior partner's former Vassal.pngvassals, Subject colony icon.pngcolonial nations, and Icon protectorate.pngprotectorates.
  • Cores on all the junior partner's core provinces.
  • 60% Local autonomy.png local autonomy in all new cores (or their previous autonomy level, if above), and 0 if the senior partner already had a core.


If the senior partner's ruler dies while the junior partner has a negative opinion of its overlord, the junior partner will become an independent nation again and be assigned a new ruler of the same dynasty. The senior partner will get a "Restoration of Union" casus belli. A junior partner can also declare war on their senior partner at any time - even while the nations are in a war together - to gain their independence. If their liberty desire remains low, then they will never declare independence. Once the player has a high enough development and strong enough army versus their personal union subject, they will never declare independence on their own, even at high liberty desire.

Note that Disloyal attitude disloyal or Rebellious attitude rebellious subjects can accept support independence offers from other countries (typically the player's enemies), which will increase their liberty desire significantly and cause them to declare a war for their independence, where the goal is for the attacker to defend its capital.


Double the Love icon
Double the Love
Start with no unions and get two at the same time.

Royal Authority icon
Install a union through a succession war.

The pen is mightier than the sword icon
The pen is mightier than the sword
Have three unions at the same time as Austria.
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