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- 1 Forming a personal union
- 2 Effect
- 3 Ending a personal union
- 4 Special cases
Forming a personal union
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There are two diplomatic actions which can lead to a personal union.
Royal marriage: If two nations have a royal marriage, and the ruler in one of the nations dies without an heir, then this is the rule of thumb:
If the player nation becomes highest total development nation of all RM partners of a nation, then the player nation will deliver a noble of their dynasty to become ruler of that nation, if their old ruler dies heirless. The total development of the player nation is shown in the country tab of the ledger.
The development of a province is the sum of its base tax, base production and base manpower. A nation' total development is the sum of all of its provinces' development values. This total development is what determines who supplies the new king for an heirless throne. However, a province with local autonomy does not have its full development counted for the purpose of this check. Hence the rule isn't absolute, but rather a rule of thumb.
So, the player nation will gain a personal union subject nation if it has higher development total then the other RM partners of a nation in disputed succession, if their heirless monarch dies. If someone contests this, a succession war will follow. It is advantageous to expand the player's nation and to increase its total development, as this is taken into account to determine whose noble succeeds to the throne of the target heirless nation. Note that it is possible to get a personal union with a succession war even without having same dynasty as the heirless nation. For that to happen a powerful rival has to be willing to start a succession war over the right to install a dynasty's noble on the throne of the target nation. At the start of the war the target nation will become subject of the contested nation.
Claim throne: If a royal marriage with a nation that has same dynasty ruler is in action, and they have a disputed succession (either no heir or an heir with low legitimacy) (weak claim), it is possible to claim their throne. Taking this action will give a -50 relations penalty to all countries the claimant has a royal marriage with, including the -100 penalty with the target. A significant benefit from claiming a throne is that it gives a claim throne casus belli to force the target country into a personal union for 84% warscore, rather than hoping their king will die without an heir. Since this casus belli always costs 84% warscore, regardless of size, it's a good way to gain large swathes of territory for little cost and almost no aggressive expansion. This casus belli disappears if the target heirless nation gets a strong heir.
There are 7 possible situations for a nation that has disputed succession. All 7 can have different outcomes, depending on whether or not the player decides to try and obtain personal unions.
- No dynasty, no heir
- No dynasty, weak heir / regency
- Same dynasty, no heir
- Same dynasty, weak heir / regency
- Succession war as defender/attacker
- Inheriting the throne
No dynasty, no heir
- The player does not share a dynasty with target nation. They have no heir.
The goal is to put the player nation's dynasty on the throne of a foreign nation to open up future possibilities, or to get succession wars over heirless nations. If two nations have a royal marriage, and the ruler in one of the nations dies without an heir, then this is the rule of thumb:
If the player nation becomes highest total development nation of all RM partners of a nation, then the player nation will deliver a noble of their dynasty to become ruler of that nation, if their old ruler dies heirless. The total development of your country is shown in the country tab of the ledger.
The development of a province is the sum of its base tax, base production and base manpower. A country's total development is the sum of all of its provinces' development values. This total development is what determines who supplies the new king for an heirless throne. However, a province with local autonomy does not have its full development counted for the purpose of this check.
If the target nation's ruler dies without an heir, there is chance to get a personal union with a succession war, if a rival of the player nation or the target nation qualifies to contest the right to have the nation as minor personal union subject.
The player can send "royal marriage" offers and later on "offer alliance" offers to two greater power nations at once in 1444, sending two diplomats on the same day, after meeting the requirements of the target nations involved. An example would be to offer alliance to Burgundy and Castile on the same day, with 2 diplomats, to avoid the acceptance malus for having multiple greater power nations as ally. Note that it is possible to have three or more greater powers as ally, if the range to them is low enough to secure a royal marriage and if player' nation has a lot of positive opinion modifiers with them. The greater powers might send offer alliance proposals to the player after using your diplomats to improve relations. This way, it is possible to have alliances with many greater power nations at once.
Heirless nations that have same dynasty in other nations won't always get same dynasty heir and won't always go in personal union under another nation of that dynasty (example: if Austria's ruler dies heirless, you can get a noble on their throne even if there are other Habsburg dynasty nations around).
To get succession wars in this step, it is strongly recommended that the player nation sets a powerful nation as rival. If not, it's impossible to get succession wars in this stage. Note that it is entirely possible to get succession wars over a nation with no heir -that is NOT of the player nation's dynasty but with whom the player nation has a royal marriage with- IF there is a greater power nation willing to aggressively contest the succession.
A noble of the player nation will become the king of the target nation:
- If player nation has highest total development of all royal marriage partners and/or
- If no greater power nation can contest the succession in any way, as stated above.
"a xxxxyan noble succeeds to the throne" it will say, looking at what the outcome of succession will be, in the target nation's diplomacy window. If they produce an heir, chances for this are removed. The player may not start a war to create a union, until the player nation has same dynasty ruler as the target nation.
The aggressive claimant of the disputed succession can change each month: usually it as a rival of the player nation, but it can also be another nation of the player nation's dynasty, if the target country is of your dynasty.
The succession status of the disputed nation will shift from succession war to a noble becoming king if the disputed nation goes to war. It is therefore a good idea to warn the target heirless nation not to go to war.
Important note: after a noble of player nation's dynasty takes the throne, it is recommended to break royal marriage if target nation is not an ally, to regain the diplomacy slot. The player nation can get succession war over a same dynasty nation when their ruler dies heirless, even without an active royal marriage with them. The player can hope for a succession war in the rest of the game, regarding this nation. This is why being papal controller is a useful tool in this context: The player can break royal marriages at will without stability hit, once the desired dynasty has spread to the target nation. Completing the diplomacy idea group also enables to break royal marriages without a stability hit.
No dynasty, weak heir / regency
- The player does not share a dynasty with target nation. They have a weak heir.
Basically, do nothing in this situation.
Same dynasty, no heir
- The player shares dynasty with target nation. They have no heir.
If a nation has a ruler of a dynasty that also rules other nations, and if one of those rulers dies without heir, then total development of dynasty partners determines who gets PU over same dynasty member. If a smaller dynasty country has a royal marriage and claims the throne, then it will switch to that country. The AI never seems to do that, but the player can. Note that a succession war can still trigger in this situation, even when having a royal marriage with an heirless same dynasty nation.
Heirless nations that have same dynasty in other nations won't always get same dynasty heir and won't always go in personal union under another nation of that dynasty (example: if Austria ruler dies heirless you can get a noble on their throne even if there are other Habsburg dynasty nations around).
The player can use the claim throne action in the diplomacy window of the target nation if he has more prestige than the target same dynasty nation without heir, and if they have royal marriage with them. The player then receives a casus belli to start a war to force a personal union with that heirless dynasty nation. If the ruler gets a strong claim heir, the player will lose the casus belli and the claim to the throne, if he did not start the war. If the player nation can win a war, claim the throne and use the casus belli to force a personal union. If winning a war would be hard, then try to become highest total base tax nation with same dynasty, and hope for succession war. Or, claim throne and hope that target nation does not get an heir before the ruler dies. If the heirless ruler dies heirless after you claimed, you usually get the personal union.
If the player nation has the same dynasty as the target nation and no royal marriage with them: if they are highest total development nation of all dynasty nations, then it is possible to get a succession war over the target heirless nation, with the player nation as defender. Setting a powerful rival is vital for this. If no one qualifies, then the player will get the union for free on monarch death in same dynasty nation if the development in player nation is high enough versus the same dynasty nation.
If the heirless ruler dies without an heir, the player gets a personal union, right off the bat, no war involved, if:
- 1.) The target nation is a small country with same dynasty and the player nation has a royal marriage with the target nation. The ruler of the target nation dies heirless.
- 2.) The player nation has no royal marriage with target nation who has a ruler of same dynasty as the player nation. The diplomacy window of target nation shows that a succession war will trigger on the demise of the heirless ruler. The aggressive claimant in the succession war is a lot weaker then the player in military rating. They can back down then, giving the player the personal union with the target nation for free. Note that it is possible to get succession war over a rival nation that also has your dynasty!
- 3.) The player nation is highest development nation of all dynasty nations, no nation will contest succession and player nation has 50% more development then the same dynasty nation.If the target nation is NOT at war and their ruler dies, the target nation falls into personal union with the player nation.
Nations can unrightfully contest this succession outcome if ONE of the following conditions applies to that nation: To qualify to unrightfully (as in aggressively through popup) contest this outcome of a succession: the player nation has to be rival of the defender, or player nation is of same dynasty as the heirless nation AND has same dynasty as the defender, or finally the player nation has a royal marriage with the defensive claimant.
If any of these conditions are met, and if any of these nations have a really high military rating, then these nations can qualify.
An example of a peaceful transition: Nation A has a ruler of same dynasty as nation B, nation B' ruler dies heirless, and nation B has a royal marriage with nation A. If the ruler of the target nation dies heirless, then nation B becomes minor personal union subject of nation A. Usually a peaceful transition is done between a big country and a really small country that is close to them. Example: Muscovy getting peaceful personal union over Ryazan, since they have a royal marriage and Muscovy has a significantly higher total development.
An example of an enemy of the heirless country being able to contest succession without having royal marriage: Poland spread its dynasty to Muscovy. The king of Muscovy dies without an heir. Poland is rightful claimant, due to having royal marriage with dynasty member, but Sweden can contest this, since they are a rival of Poland. Succession war will decide if Muscovy goes under Poland or Sweden as minor PU slave.
Important note: It is possible the player gets an event that can lead to a peaceful union of two nations if event conditions are met. Both rulers must be between 16 and 40, the two nations involved must be neighbouring each other, both nations must have no heirs, both rulers have to be of different sex and be either of the same dynasty or in the same culture group. Both nations need to have high enough opinion with each other. The MTTH of the start is 500 months. Portugal can get a UNION over Spain this way, Or Styria can get a Union over Austria. This event can also cause a personal union between two non christian nations.
Same dynasty, weak heir / regency
- The player shares dynasty with target nation. They have a weak heir/regency.
The player can use the claim throne action in diplomacy window of the target nation if he has more prestige than the target nation at that time. The player receives casus belli to start a war to force a union. If the ruler gets a strong heir, the player will lose the casus belli and the claim to the throne, if he did not start the war. If player nation can win a war, then use the claim throne button in the diplomacy window of the target heirless nation, and use the casus belli to force a personal union.
Succession war as defender/attacker
- The player nation and a third nation qualify for succession war.
A succession war can trigger if there are 2 sides who can contest the succession, meaning:
- The rightful royal marriage/dynasty claimant (rightful, meaning: they got royal marriage and/or same dynasty with heirless nation; or they don't have royal marriage with the heirless nation but they got highest total development of all dynasty partners)
- The aggressive claimant (this nation is chosen among the player nation RM partners, their rivals, and all dynasty partners of the heirless nation). What nation is chosen among the possible nations is based on the military rating (see score system to read on what is included in the calculation of the player nation's military rating) of the eligible nations that can contest the succession, and this nation can change each month (since a nation that is losing in a war can drop a lot in military rating)
A succession war erupts if the ruler of the target nation dies heirless, and if two nations qualify to wage succession war. The most powerful country in military rating that can contest the succession outcome aggressively will get a popup window that gives choice between enforcing their aggressive claim with a war, or to back down. The possible aggressive claimants are: the player nation RM partners and rivals, and the nations that have same dynasty as the heirless nation. This means that if the player is the rightful claimant, this aggressive claimant might declare war to take the freshly installed personal union away from the player for their own. And there will be no popup, the succession war will start whenever the involved heirless king dies. There is no way for the player to avoid this war. If the player qualifies to contest that their rival places a noble of their dynasty on a foreign throne, a pop up will appear asking the player whether or not he wants to aggressively contest the succession.
What happens next?
- The DEFENDER (the rightful claimant) gets the target nation as a personal union subject at the start of the war, but the player, his allies, and the new subject nation need to fight a rival nation/other claimant over the right to have the nation as a minor personal union subject. All the allies of both sides can get called to war when this aggressive claimant declares war on the player.
- The ATTACKER needs to fight the defender nation, the target nation who will be subject to them, and all their allies. This attacker can call in their allies in this situation too. Beware however, that if the aggressor's allies have a truce with the rightful claimant, they will not join the war, leaving the contestant alone against the union's allies and vassals.
If defender, the player nation will go to war when heirless ruler dies of the target nation. If the player gets the popup to choose to contest the succession: only attack if player nation and their allies can win war against heirless nation, the nation that gets the target nation as subject and it's allies, otherwise don't press.
Inheriting the throne
- The player nation can inherit personal union subjects every time their ruler dies.
The chance for this is shown in the diplomacy window of the personal union subject.
- The player nation can also inherit a nation that has same dynasty .
The player nation can inherit another nation outright if their total development is big enough (>50%) versus the total of the heirless dynasty partner nation. If player nation inherits a nation, they get immediate cores on all the provinces of the nation they inherited, and all their subjects are set free. The colonial nations of the inherited nation become subject of the nation that inherits them.
- A nation can have an heir in regency. If that heir dies by event, the nation can go in interregnum if no new heir spawns.
The player nation can do royal marriage with this nation, if none exists. Of all the royal marriage partners of the nation in interregnum: the nation with the highest total development will deliver the new ruler to the nation in interregnum. The player nation can get a free dynasty spread and a chance at claim throne/force PU war as soon as the noble of their dynasty takes the throne of the nation in interregnum.
- The game of thrones in Europe and beyond is a lot more complex than just disputed succession. This game of thrones is a hidden aspect of the game, that nevertheless can give the player the most territory gain for a world conquest attempt.
- Playing the claim throne and royal marriage game means keeping prestige at near hundred all the time, never giving in to rebels, to keep the prospect of claiming foreign thrones. The player has to adapt their gameplay: keep conquest (to obtain higher total development) and rebels balanced. Humanism is a great idea group to prevent rebel problems on non accepted culture provinces.
- A nation can grow strong when they gain a personal union with a greater power nation. Like France getting Castile as minor personal union subject. Play this game, and Castile could have been the player's personal union subject. What the AI can do, so can the player.
- important tip: message settings are crucial for this game of thrones. First and foremost, and this might be the most neglected aspect of eu4. Hidden popup and pause messages that the player can enable, that are off by default. In message settings select "all" tab and enable the popup and pause for every herald possible for *every option" in the "to me", "from me", "interesting" and "other" categories. Then, in the window above the map buttons select interesting nations. In short: select all nations in the religion group of the player nation, since the player nation can't get personal union over a nation that is not in their religion group. The result is that the player can perfectly see when a new king comes to power, or when an event takes place that kills an heir of a nation.
Example: Enable minor and major event popup and pause for interesting countries, for any event they get. Why? If that interesting country has 40+ king with a regency heir for example, and the target country gets the event that might kill their heir, the player can see the outcome right after. No more AI personal unions being installed without the player having a clue.
The player can then later disable the popup and pause for unnecessary message types (like what country gives military access to another) by changing it in the popup window (options at right bottom). Some important popups the player should enable for popup and pause: when armies arrive at destination, when country gets new king, major and minor events for any nation, diplomats arriving back home, traders arriving back home, what country gets succession war with another, when a country starts integrating a vassal and so on and so forth. Prepare to read ton of stuff, the player can disable this but might miss out on easy dynasty spread chances when a country' heir dies due to event.
- Note that an heir of a country can die during combat, sieging or just of natural cause as well, and the player will not receive a herald popup and pause for this. Here comes the disputed succession window in handy, to check if there is any heir dead (that a country went to disputed succession status without you getting notice from herald). Prepare to look at diplomacy of many countries frequently, or its easy to miss out on easy RM and dynasty spread partners.
NB: since 1.2 the CB is now only granted when claiming the throne of a country with the same dynasty as yours.
NB: since 1.7 You can only claim the throne of a country that is the same dynasty as yours.
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, you do not receive any income from lesser partners in a personal union.
Ending a personal union
A personal union can end in several ways. Either with the incorporation of the junior partner in the senior partner, with the junior partner declaring their independence, with negative prestige number when your current ruler dies, with negative opinion modifier of the target nation when your current ruler dies, with pretender rebels enforcing their demands in the target nation.
Integration & inheritance
After 50 years the overlord nation can inherit or integrate their personal union subjects IF the overlord has more provinces then the PU subject nation. Inheriting the PU subject can occur each time the ruler dies. This chance may be 0%; to see the probability, hover over the king in the diplomacy screen. The main factors for inheritance chance are Diplomatic 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.
Alternatively, if the senior partner has over 190 relations with their junior partner, they can take the diplomatic action "Integrate" to immediately start the process of integrating them. This process works identically to annexing a vassal, and the diplomat cannot perform any other missions while integrating. You may cancel the diplomat, but all progress and diplomatic power will be lost, so this is generally not recommended. To see the modifiers, progress, and remaining time, hover over the icon in the diplomacy screen or in the outline once integration has started.
Either way, integration will end with the senior partner owning all the junior partner's territory and gaining cores on all the provinces the junior partner had a core on, as well as being the new overlord of any vassals, protectorates, or colonial nations the junior partner may have had. If the junior subject has uncored provinces, the senior partner gets control of those provinces, but does NOT get a core on those provinces.
Rebels that change government type or state religion and enforce their demands in the provinces of the junior partner being integrated may instantly cancel the annexation process and even break the Personal Union.
Note: Player-controlled nations will never be inherited on monarch death, though they may still be integrated manually by their overlord.
If the senior partner's king dies while having negative prestige or negative relations with the junior partner, the junior partner will become an independent nation again and be assigned a new king of your dynasty. The senior partner will get a "Restoration of Union" casus belli to reclaim the throne for 60% warscore. A junior partner can also declare war on their senior partner at any time - even while the nations are in a war together (since the 1.6 patch) - to gain their independence. Note that, since the 1.6 patch, a "great power" nation which is the lesser partner in a personal union is far more likely to declare a war for independence. If you manage to keep their liberty desire low, then they will never declare independence. Once you are big enough versus them they will never declare independence, even at high liberty desire. But subjects can ally with one another and ask "support independence" from other nations. In such cases, the player nation can face a huge independence war involving many subject nations and enemies that support their independence.
If the country creates personal union as a leader with another country which is leading its own personal union, also the junior partner's junior partner will enter the personal union. Example: Aragon is leading personal union with Naples and Castile creates personal union with Aragon as a leader, Castile will lead personal union with both Aragon and Naples.
Personal unions and the republican government
Although personal unions are institutions related to monarchies both in-game and in real history, republics may also form them, even if extremely rare. As of 1.12, the union controlled by republic has the same conditions of continuation as the normal one, no matter if the ruler dies or gets voted out of office. The only republic types that offer better chances of creating a union (and some control over them) are noble and Dutch republics. The Dutch republic may also get an event-triggered union forming CB that reflects such historical case.
A junior partner of the republican personal union will cause the ruler to receive their cultural dynasty name that will change every time the ruler changes
A republic may never be a junior partner in a union.