I've been in alliances with races, but what is the purpose, other than they're very friendly? Can I ask them to go to war with common enemies with me? I know I can always ask a civ to attack someone, but it all seems to depend on their own relations. In other words, if I'm allied with civ A and I want to eradicate civ B, but civ A and B are neutral or higher toward each other (but not allied with each other), I can't get my alliance partner to help. It's not even an option to attack them in negotiations.
Also, is there a way to ask your friends or allies to enact trade embargoes against a common civ? These are things I know I can do in Civ IV, but am having trouble figuring out in GalCiv II.
And are there any "special negotiation options" you gain from being allies?