Personal unions in Europa Universalis 4 are a bit of a mystery. The game manual doesn't even mention it and most players haven't figured the mechanics out. To be honest I didn't really understand it until recently.

Not understanding personal unions at all can cause some problems when you're playing a game of Europa Universalis 4. A while ago I "suddenly" became a minor partner in a personal union with France. It basically ment the end of the game I was playing. Obviously a bit depressing if you don't have a clue what just happened. But with this miniguide you don't have to suffer the same fate as me!!!! In the worst case scenario you understand what went wrong.

What happens in a personal union is that a ruler (let's call him Charles IV in this example) steps in when his dynasty member (read: neice, nephew, brother, etc.) dies. Charles IV can demand to become heir of the country, if his dynasty member doesn t have a proper heir. In a succesfull personal union Charles IV will replace the current unsuitable heir (an heir is unsuitable when he only has a weak claim). Charles IV can also become the heir if there is no heir to the country.

Charles IV will end up ruling both countries. This is what a personal union is. The person Charles IV ends up ruling 2 countries because of his family connections.

The junior partner in a personal union acts very much like a vassal of the major partner. The major advantage of having a personal union compared to having a vassal is that you can control more sizeable countries with a person union. It is generally easier to vassalise smaller countries than to engage in a personal union with them!!!!

The hardest requirement to meet for a personal union claim is that your country and the country you want to engage a personal union with need to be of the same dynasty. At the start of the game there are probably one or two countries that have the same dynasty as yours.

You can check what countries have the same dynasty as yours by hovering over your rulers name. In this picture Castile has the same dynasty as Aragon and Naples.

But you obviously want more control than that!!! This raises a question: How do I change a country's dynasty to mine? Dynasty changes only happen if a country's ruler dies without an heir. So this makes dynasty changes a rare occurance at best. Let's hope paradox creates a DLC that allows you to kill kings or their heirs sometime!!! If a ruler dies without heir, a noble from another dynasty will take the throne. The noble that gets picked will be of the dynasty that has a royal marriage with the country. If there are multiple royal marriages the dynasty with the highest prestige will provide the noble.

It is also possible that the death of a ruler leads to a personal union and triggers a succession war. If you win this war you will have established a personal union with the target. When you will end up in a succession war or when your dynasty member becomes the new ruler is not completely clear. But after much experimenting I managed to make a list of situations where you would get a noble to become the new ruler (and not a personal union with a succession war). If one of the following is true a noble will take the throne:

• The country is someone's vassal
  
• The country has no royal marriages and there are no other independent rulers with the same dynasty
  
• The country is leading a personal union
  
• The country is at war.
  
• The government type is not a monarchy

In all other cases you can assume the target country will end up in a succession war when their ruler dies. This seems to be true in most (>90%) cases.

Note how Portugal has no heir. The throne will be inherited by someone from the dynasty "de Trastámara", because that is the only dynasty they are royally married with. The current ruler is of the "de Avis" dynasty.

In order to create a personal union you need to get a claim on the throne first. To accomplish this you need to meet several criteria.

• Monarchy: You and the country you want to create a personal union with need to have a monarchy. Quite logical if you realise personal unions are based on familly related claims. This obviously wouldn't be possible in a more democratic system.

To check the government type of a country rightclick any province and look at the highlighted icon. if you see the little crown like in this example, you are dealing with a monarchy.

• Same dynasty: You and the county you want to create a personal union with need to be of the same dynasty. This represents being family-related with each other. More about this in the dynasty part of this miniguide.
  
• Royal Marriage: Both countries need to be royally tied to eachother by a royal marriage.
  
• Weak/No heir: The country you want to create a personal union with needs to have an heir with a weak claim or no heir at all. If they had an heir with a strong claim (like the son of a ruler) you couldn't claim you should rule the country.
  
• Prestige: You need to have higher prestige than the country you want to claim the throne from.

After meeting the criteria you can get a claim on the throne in the diplomacy menu. You will get the "Claim on Throne" casus belli with the target country. But you can also lose the "Claim on Throne" casus belli again. This happens if:

• The royal marriage with the target country ends. Royal marriages usually end if one of the rulers engaged in the royal marriage dies. So don't worry about this one too much. Just don't use diplomacy to end it. When you declare the war you will have to take the -1 stability hit for declaring war on someone you have a royal marriage with.

After you get the "Claim on Throne" casus belli you can declare war on the target country. You will have to defeat them and their allies to successfully create the personal union.

As mentioned before there is also another way to get a personal union. Remember when we were talking about changing dynasties? If a noble didn t take over the throne, someone ends up in a succession war instead. Of the people who were elegible to inherit, the one with the highest military rating will become the major partner in the personal union.

You can check the military ratings of different countries in the ledger. You can find it by clicking "score comparison" within the "country" submenu of the ledger. Click on military rating to order the list based on the military rating.
Example: If Austria, Burgundy and Portugal would have had a royal marriage with France. Austria would inherit France in a personal union if their ruler died without succession.

So what happened? Why did a war start all of a sudden? You inherited the throne and not some random noble!!! Your rivals will not like what has happened. Therefore your strongest rival or someone, who also had a chance of inheriting, will declare war on you directly after you inherited the throne. The country that starts the war against you is the one with the highest military rating. If you happen to play the competing country you will get a succession war casus belli for the personal union.

The personal union technically was established before the war started. So the troops of the minor partner in the personal union will help you as your "vassal". The goal of the succession war is to own the capital of the minor partner in the personal union. Controlling it will give a ticking warscore.

If your rival wins the war he will become the new ruler of the contested throne. If you manage to peace your rival out without enforcing you to transfer the personal union to him, you will have maintained your personal union. If you would accept the peace offer in this picture you would transfer the personal union with Navarra to your rival Aragon. Also note that the highlighted tooltip isn't correct but the description in the box is.

After establishing the personal union you still do not own the lands yourself. Instead the junior partner in the personal union is a vassal that doesn't pay you taxes. The lands can become yours after 50 years. Then you can decide to annex it or hope to get lucky and inherit it (for real this time :p).

Keeping your personal union

So after establishing the personal union your job has become to maintain it for at least 50 years. Of course this wouldn't be much fun if the minor partner in the personal union didn't have a chance of breaking free. There are several ways this could happen:

• Your minor partner revolts Your minor partner can revolt against you and try to get enough warscore to declare independence. This should not be a very big problem to deal with, unless you are really beat up from some war and they aren't.
  
• Ruler dies with negative prestige: If the ruler of both countries dies with negative prestige the personal union will end. Keep this in mind when dealing with prestige related events and wars.
  
• The minor partner has a negative opinion of the major partner on rulers death: If the minor partner in the personal union has a negative opinion of the major partner and the ruler dies the personal union will end. If you are playing the major partner make sure to keep good relations with your minor partner. If you send your diplomat frequently to keep relations in good shape it is very, very unlikely to lose your minor partner this way. If you are the minor partner this is the easiest way out. Try whatever you can to ruin your relations. Insult them and go to war for independence, even if it is just to mess up your relations.
  
• A country demands you release the minor partner: If you lose a big war against anyone, your enemy can demand that you release your personal union partner in a peace deal. If this happens they will become independent again. The new ruler will still have your dynasty.

Integrating your minor partner in the personal union

After 50 years you can integrate the minor partner of the personal union. The process is simular to annexing vassals. It will take 1 month to integrate each base tax the target country has. During the integration you will consume 15 diplomatic power for each basetax point (that makes 15 diplomatic points/month provided you have enough). You can only integrate countries that own less provinces than you.

Inheriting your minor partner in a personal union

If your ruler dies you have a small chance of inheriting the lands of the minor partner in the personal union. This is only possible after keeping the personal union stable over 50 years.

If you hover over the name of the ruler of the minor partner inthe personal union you can check what the chance to inherit the lands on death of your monarch is.

Usually integrating your minor partner is easier that hoping to inherit it. Inheritance chances are usually pretty low. If you are playing as a minor partner you can not be inherited. Inheritance chances are modified by:

• Country size: The inheritance chance will be decreased by 1% for each province the minor partner owns.
  
• Diplomatic reputation: You get a percentual increase of 2 times your diplomatic reputation. So 5 diplomatic reputation would increase inheritance chances by 10%. This is the main source to increase inheritance chance. You can increase your diplomatic reputation by having certain ideas, advisors, having high legitimacy, etc.
  Stability: Each positive stability point increases your inheritance chance by 1%.

Inherit a personal union

• Royal marry potential personal union targets.
  
• Hope their ruler dies without heir and a succession war starts
  
• Win the war or peace out without losing the personal union
  
• Keep the personal union stable for 50 years
  
• Annex or inherit the targeted country

Claim a throne

• Royal marry potential personal union targets if they are not your dynasty
  
• Hope their ruler dies and make sure someone of your dynasty becomes the new ruler
  
• Hope the ruler with your dynasty ends up with no heir or a weak heir
  
• Claim the throne
  
• Use your "claim on throne" casus belli to declare war
  
• Win the succession war and demand the personal union
  
• Keep the personal union stable for 50 years
  
• Annex or inherit the targeted country

This guide is made based on version 1.7.3 of Europa Universalis IV. If you are using a newer version things might have been slightly outdated (but the mechanics will probably be the same!!!)

I tried to figure out most mechanics by trial and error, since there is little to no information about personal unions on the internet. From what I have seen those mechanics seem to be working as I described. If you find out something that isn't correct or isn't in the guide (and should be) please comment!!!

If you see anything that is missing and should be in here or have anything else to say about this minguide please leave a comment.