An alliance will go nowhere if it becomes an island unto itself. It's the interaction with other alliances that really determines where the game goes.

You need good diplomats, and guys that can negotiate well with the other alliances. It's often hard to understand all the inner mechanics of world events, but you have to be aware of what's going on.

You have to be able to trust the people you are with. If you're paranoid, then your alliance will tear itself apart. If you're too trusting, then you will be taken advantage of.

You also need to be good at conflict resolution. If you have to resort to expelling troublemakers consistantly, you will have problems growing.