Common Ally with Enemy

[Granite]

I want to start a war, but empire I am going to attack is allied with my ally. Will my ally attack me to defend my enemy?

[HappySack]

It should show who will be involved in the war declaration screen if you were to declare war, but if I were to guess then yes.

[Sero]

I dare say it depends on the relationship they have to you and your enemies and what kind of pacts they have with each of you.

[Granite]

Well the Mushroom Empire needs to grow so let's try it out. I'm going to beef up the fleet a bit if the ally gets froggy and jumps me

[Mennan]

Yeah just test the waters by hitting the declare war button and at the reason screen it will tell you if your ally will defend him. If your ally is simply in a Non-aggression pact with you but defensive pact with him he will probably side against you.

[Ryika]

The game doesn't have Alliances, so you don't have Allies.

What the game does have is defensive pacts, and they work exactly as the name suggests: If a person is attacked, the other person will join the defensive war.

Since you're the aggressor, your Defensive Pact with the third party does nothing, but since they're the defender, you'll find yourself in a war with both of them.

[RawCode]

your "ally" will join war on defender side
same will happen if other party attacks you

this will override truce and few other conditions, in some cases allowing war declaration when normally this is not possible.