What causes empires to attack other empires?

I like to ally every empire I meet, but sometimes my allies will fight wars with each other, constantly nagging me to help them against each other and becoming angry that I didn't. What causes AI empires to go to war with each other and how can I prevent it?

Solution 1:

Their personalities is the main factor in deciding who they war with. An empire that starts off distrusting you (the -30 for 'we don't like strangers') will be much more likely to be at war with other empires. Now this is just a theory, I don't know of any way to confirm it.

You also cant stop warring empires from going at it, even if they are a part of your alliance.

Something I do when my allies are fighting with each other: I will go to the distressed planet, but wont engage in any combat. Usually the defending planet will be able to win without help (as they respawn ships). Still get successful defense rewards, and nobody is mad at me, because according to the nation who called for help; I was there and 'helped'. and the empire that attacked doesn't get angry at me for killing any of their ships.