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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.
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)
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.
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.
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).