I have played a great many games, but most of the time only until I defeated one or two factions, because then I was so far ahead that I lost interest in the game. So I never paid much attention to alliances.
But in my current game I managed to become second best after defeating the first AI, but the best AI has the quadruple power rating than mine (about 22000 against my 6000). So I allied with six other AIs until the most powerful AI declared war on me. But now I have to fight alone (and I am losing right now), all the others do nothing.
So my somewhat noobish question: how do I bring my allies to honor the alliance and fight on my side?