This is probably a rather dumb question, but there is no section in the manual that describes victory conditions.  That strikes me as a dubious choice for a manual, but anyway...  I assume there is no section of the manual talking about victory conditions because the primary one is "kill everybody else".  But in my current game I've eliminated one faction and have 100% relations and all the treaties with the other two.  Is there no such thing as a diplomatic victory?  Am I forced to declare war on my allies one after the other until no one is left?

If that's the case it makes one wonder why anyone would ever make an alliance with you...