What are the requirements to join a war

[Grothgerek]

Hi everyone,
for my next multiplayer RP game I plan to build a mercenary faction.
There are many ways to influence the galaxy, for example selling guarantees, non-aggression pacts or start separate wars.

But there is a even better feature: you can ask other empires to join a war against a enemy. But you can't invite everyone. There seems to be a requirement to show up.

Does anyone know what these requiremts are? Rivalry? Claim? Negative opinions? Shared Borders? Sadly I couldn't find anything on the Wiki, and if I use Google most people just ask to join a war after it already begun (which isn't possible).

It would be nice if just creating a claim, or even better just insulting someone, makes me applicable to be ask to join (for the right price xD).

 

[hart30]

I believe it mainly comes down to ur future allies opinion to u and ur opinion/ur enemies/allies opinion to ur enemy. Pacts, claims or rivalry are just ways to move opinion in the right direction.

After this there are two more factors. Is ur future ally already in a war or a crisis ongoing - then they wont join. Is the powercalculation too far off? Then they wont join. Even when the checkmark shows up as green.