Probably one of the most powerful mechanics in EU4, the personal union is the best and simplest way to conquer the whole world! You will also need to know how to use them if you want achievements such as Royal Authority, The pen is mightier than the sword, and Atwix Legacy. So, here is an extensive guide on how personal unions work in Europa Universalis IV, and how to best utilize them.
How Personal Unions Work in EU4
Personal Unions are a very powerful mechanic that can help Christian nations rule over other big countries as if they were vassals. This technique can be used to conquer huge amounts of land without the usual repercussions.
Usually, Personal Unions in EU4 trigger when a kingdom’s monarch dies without an heir, while also being in a royal marriage. Players can also gain a union with a country if they gave a claim to the throne.
If it wasn’t obvious, Sunni, Hindu, Confucian, and any other non-Christian countries can’t use the EU4 Personal Union mechanic, even though they have access to royal marriages.
Something unique for Personal Unions is that the junior partner of the union can also have its own vassals. Those are gained before the union though. Also, the senior partner will not receive any taxes from their “vassal”, but, other than that, they work in every way as a normal vassal.
Players can use all the normal subject interactions (found in the Subject tab) that they use with vassals with the junior partner as well. Nevertheless, EU4 fans will be able to integrate (annex) the lesser part of the Personal Union only after 50 years of vassalage.
How to Form a Personal Union in EU4
There are 4 ways players can get a Personal Union in EU4:
- Through Events
- Through Missions
- Through Diplomacy
- Through War
Personal Union Events
There are many countries in EU4 that can get a Personal Union very easily through special events. These are the countries, with their respective events and junior partners:
- Poland → Can form a PU (Personal Union) with Lithuania during the “Successor of Wladyslaw III” event.
- Castile → PU with Aragon (and Naples) in the “Iberian Wedding” event.
- Aragon → PU with Castile in the “Iberian Wedding” event.
- Aragon → PU with Navarra if Joan II gets the throne in both countries.
- Spain → PU with Portugal in the “Portuguese Crown” event between 1550 and 1650 (Extremely Rare).
- France → PU with Naples (Naples gets the event).
- England → PU with France by winning the war caused by the “Surrender of Maine” event.
- Brandenburg → PU with Prussia if the relation is over +100.
- Brandenburg → PU with Ansbach if Albrecht Achilles gets the throne.
- Austria → PU with Hungary in the “Death of Ladislaus Postumus” event.
Personal Union Missions
Some countries have the extreme luck of having specific missions that will let them create Personal Unions. To clarify, here is a list of all the kingdoms that can form Personal Unions through missions, and their potential junior partners, in EU4:
- Aragon → Portugal
- Austria → Bohemia, Poland / Commonwealth, Hungary, Bavaria, Milan, Naples / Two Sicilies
- Bavaria → The Palatinate, Brandenburg, Austria
- Bohemia → Hungary, Poland / Commonwealth
- Castile / Spain → Portugal, Austria, England / Great Britain
- England / GB → France
- France → Castile / Spain, Naples
- Franconia → France, Brandenburg / Prussia
- Hannover → England
- Hungary → Bohemia, Austria, Naples, Poland / Commonwealth
- Lithuania → Muscovy / Russia, Poland
- Milan → Naples / Two Sicilies
- Navarra → France
- The Netherlands → England / GB
- The Palatinate → Bavaria, Bohemia
- Poland / Commonwealth → Hungary, Bohemia
- Provence → Hungary, Naples, Aragon
- Savoy / Sardinia-Piedmont → Corsica, Sardinia, France, Sicily, Naples / Two Sicilies
- Saxony → Poland / Commonwealth
Personal Union Through Diplomacy
For 2 countries to enter a Personal Union, some conditions must first be met:
- The potential junior partner has to meet all these requirements:
- Has no heir
- Is not a senior partner
- Is at peace
- The potential senior partner must meet one of these:
- Has the same dynasty as the potential junior
- Has a royal marriage with the potential junior
- Has claimed the throne
Now, all that needs to happen is for the potential junior partner to lose its ruler. When this happens, based on these criteria, the priority of who will get senior partnership will be in this order:
- Country with a claim on throne
- Country with the same dynasty
- Country with a royal marriage
If 2 EU4 countries are at the same level of priority, the one with the highest development will win the Personal Union.
The country that was second on the PU succession line will receive an event that will let them declare a Succession War. This will allow them to subjugate the junior partner under themselves and release them from their original master.
Succession and Personal Union Through War
Attacking another nation under one of the three casus belli—Force Union, Claim on the Throne, or Restoration of Union—can result in the formation of a Personal Union between the two nations.
If the target nation shares the same dynasty as the target nation, has either no heir or an heir with a weak claim, and has a royal marriage with the nation, the Claim on Throne Casus Belli can be obtained by taking the Claim Throne diplomatic action.
The claim will expire if the target nation acquires an heir with a strong or average claim, or the royal marriage used to secure the CB terminates for whatever reason if the country has obtained the CB in this manner.
Take note that breaking an alliance will result in a 5-year ceasefire. Breaking the royal wedding would result in the loss of at least 1 stability since you cannot break the royal marriage without losing the CB.
If a junior partner in a personal union leaves, senior partners may get the Restoration of Union CB. Usually, in the event that a monarchy with whom a nation has a royal marriage introduces a new heir, the country may also get a Restoration of Union CB against that kingdom.
The player must launch an attack against the target nation using one of the aforementioned casus belli to enforce the claim. The objective of either CB is to take control of the target nation’s capital, and enforcing the union incurs a war score cost of 84% or 60%, irrespective of size.
Aggressive expansion relative to the size of the target country will result from this. In addition to the possible 100 opinion modifier brought about by seizing their throne, enforcing the union will also result in a 100 opinion modifier with the new subject.
And that is all there is to know about the personal union in EU4. Check out other interesting guides and articles:
- EU4 (Europa Universalis IV): How to Release Vassal
- EU4 (Europa Universalis IV): All Achievements List – Requirements
- EU4 (Europa Universalis IV): All Formable Nations – Requirements
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