An alliance is an agreement between two rulers that they can call upon or join each other's wars via a character interaction. Declaring war on an ally will add -25 Popular Opinion for 3 years.
Creating an Alliance
An Alliance is created automatically between two characters who are married, it is also created automatically when two close family members of the two rulers are married or betrothed to each other. It is possible to see whether the marriage proposal will result in an alliance on the marriage proposal screen. In addition, two Rulers can negotiate an Alliance if one of the following requirements are met:
- The ruler is your child, parent, or sibling
- You are married to a child, parent, sibling, grandchild, grandparent, uncle, aunt, niece, or nephew of theirs
- They are married to a child, parent, sibling, grandchild, grandparent, uncle, aunt, niece, or nephew of yours
- Their child, parent, or sibling is married to a child, parent, or sibling of yours
- One of the rulers has the Defensive Negotiations diplomacy lifestyle perk
The acceptance of an Alliance is determined by the difference between the tiers of the two ruler's primary titles, the difference in military power as well as their Opinion of each other. In addition the acceptance can be affected by the following:
A proposed Alliance can be accepted by using a Hook, either Weak or Strong.
When a character is at war, each one of their allies will have the option to join the war via the Offer to Join War character interaction, which the targeted character will always accept. Alternatively, a character who is at war will have the option to ask their allies to join a war via the Call to War character interaction. The acceptance is determined by the character's Opinion, modified by the following:
|Defensive War against their Ally||-25|
|Offensive War against their Ally||-50|
|Enemy is Heir||never|
|Enemy is Spouse||never|
|Rank||Cost ( Prestige)|
Allies declining a call to war invitation will suffer an opinion penalty with their ally (-10 for one year for offensive wars; -20 for three years for defensive wars).
End of the Alliance
The alliance ends immediately after the requirements listed in "Creating an Alliance" are not fulfilled anymore. Ongoing wars are not affected.
game\events\interaction_events\alliance_interaction_events.txt. Barons, along with empires, cost
massive_prestige_valueto call (likely a bug).