It depends on whether you're going for a win based on wiping out the guys who aren't in your club, or actually making peace with everyone without wiping anyone out. But Terrans are a sure bet, especially with their Super Diplomacy ability. The more you pump your Diplomacy ability, the easier it will be to bring wars to an end, or get others to start them if need be. You'll need a great economy to keep handing out bribes... I mean, generous donations in the name of peace.
You can win an Alliance victory without a fleet, but it is much easier if you actually have the muscle to back up your hustle.
