This article is accurate for the latest versions of EU3, Napoleon’s Ambition, In Nomine, Heir to the Throne and Divine Wind.
A Personal Union (PU) exists when a single monarch rules two nations but has not yet inherited and merged the nations outright. In this arrangement, one nation is the Senior partner and one the Junior partner. Only the Senior may declare war, make peace or arrange royal marriages. Since there is only one king, the two nations are automatically allied with each other. While in a union, both nations experience positive relations bonuses similar to that received by vassals.
A Personal Union can only occur between nations meeting the following criteria.
- Government must be a Monarchy
- Be in the same Religion Group
- Not be a junior partner of either a vassal or Personal Union.
Setting up a PU
There are three approaches to set up a Personal Union with another nation.
- Royal Marriage: After setting up a Royal Marriage, if their monarch dies without an eligible heir, and you have the highest Prestige amongst their Royal Marriage'd nations, one of three things may occur. A monarch of your dynasty will become the new monarch boosting your relation and chance for future diplomatic actions, they enter a Personal Union with you, or an immediate inheritance.
Tip: The last one may happen even if they're your vassals, so be careful when you use Royal Marriage with your vassals.
- Fabricate Claims: If their monarch has <50 Legitimacy, or they don't have an heir of >33 Legitimacy during a regency council, you can use a spy on their capital to produce the Obscured Document CB. Simply use said CB, and enforce the Personal Union through the war demand.
Tip: Reducing enemy Legitimacy through high War Exhaustion is a good way to follow up with Fabricate Claims.
- Claim Throne: If the target is in a Disputed Succession (indicated as warnings at the top of the screen), and you have enough Legitimacy and Prestige to do so. Simply set up a Royal Marriage, and use the Claim Throne diplomatic option to trigger the effect. Once done, either hope that their monarch dies before producing an heir and go into a PU, or declare war use the Claim Throne CB produced the 1st of the next month and apply Personal Union as the war demand. As long as the war is declared before they gain a new heir then the final demands are valid, this means that a quick declaration if often worth the risk.
Tip: As subsequent Claim Throne will reduce relation with all nations having a RM with you, it's recommended to cancel the Royal Marriage before going to war if you have spare diplomats and time so you won't have to rebuild your relation with nations already in a RM with you (nations already in a PU with you are unaffected).
Tip: Being a Papal Controller can remove the stability hit for canceling a Royal Marriage
If your relations with your partner are above 0 (possibly above 100) and your prestige is positive, you have a certain chance to inherit them every time a new ruler takes the throne as long as your country is larger than the Junior country. Inheriting a small nation appears to be more likely than inheriting a large nation. Also, it seems you cannot inherit during a war. Unfortunately, the mechanics behind inheritance and which factors influence the inheritance chance are not very well understood by the community. What is known is this:
- The diplomatic skill of the new ruler (heir) is very important; 3 or lower and you probably won't inherit, 7 or higher and you very likely will.
- Higher Prestige helps (needs to be >0, or you lose the PU)
- High relations help (needs to be >0, or you lose the PU; needs to be >100 to have an inheritance chance at all)
- High BB lowers chance to inherit, but has no impact on losing the PU
- Trust has a very high impact on inheritance chance: see this forum post
Additionally, these things are thought to increase an inheritance chance, but they have not yet been proven, or disproved:
- A ruler's DIP rating increases inheritance chance
- Being at war no longer seems to prevent inheritance (DW)
If you have more than one country in PUs, only the one with the highest relations can be inherited. If multiple countries share the highest relations, you may not be able to inherit any of them.
Inheriting and Cores
You receive cores on all provinces that are in your culture group upon inheritance. If you are playing Divine Wind, and both countries are in the HRE, you gain cores on all HRE provinces, no matter the culture group. You do not gain cores on non-HRE provinces that are not of your culture group. These cores will preserve all buildings in DW.
As of Divine Wind it is possible to integrate a lesser partner after fifty years of union and when relations are over 190. Contrary to regular inheritance, it doesn't grant you cores on acquired territory even if it's inheritance inside the HRE or inheritance of your culture group provinces. For those two cases it's more beneficial to wait for normal inheritance and get cores on provinces right away.
Getting out of a Personal Union
If you end up being the minor partner in a Personal Union, you'll probably want to get out of it as quickly as possible. There are a couple of ways to return to being an independent kingdom.
If the diplomatic relations between the Junior and Senior partners in a PU are negative, the Union will end when the current monarch dies. This is not so hard to achieve, since insults are free (besides the 1 diplomat and one prestige). Each Insult reduces your relations by 50.
While this solution is free, it might take a while, as monarchs can sometimes rule for several decades.
EDIT: Or at least other countries' monarchs usually rules for quite long, particularly if you are in line for the HRE throne or you want out of a personal union. Your rulers die like flies.
Pretender taking over
If pretender rebels pop up, there are two distinct ways to get out of a Personal Union.
- Giving in to rebel demands
- Allowing them to successfully take over
Both options will make the pretender the new leader of your nation. Note, however, that the pretender will also make several slider moves, often to Decentralization and Serfdom. This solution will also decrease stability.
If you change your form of government to a Republic, the Personal Union is broken. The cost is a decrease in stability. On the other hand, republics are rather effective.
Heir to the Throne introduced a new and more direct way to escape a personal union. Break the alliance with the senior partner and simply declare war. If you win, you'll be a free nation again. Especially useful when you end up in a union under a much smaller nation, or start the game in such a situation (e.g. Holland under Hainaut, Brandenburg under Luxembourg, Sweden under Denmark).
You'll have to take the stab hit for war without a CB. Also, keep in mind that you might also have to fight the senior partner's allies (and possibly the Holy Roman Emperor).