How do I make ALLIANCES?!?

For the life of me, I can't figure out how to make an alliance in this game.  I fully research diplomacy, I set up trade, I give gifts, and yet I never have the option under the treaties tab to request an alliance!  The only options that ever appear under the treaties tab in foreign diplomacy is to either declar war or make peace.  What button am I missing that allows me to forge an alliance?  I'm beginning to think that alliances don't even exist in this game, seeing as how I've played it many times through and have never been able to forge a single alliance with anyone no matter what I try.  Any advice I ever get about alliances tell me all the stuff I already know, but they don't tell me the exact button I click to get there.  Don't give me strategies, I want to know where to click!