In my last DA game I tried to create two teams at the game setup stage: one evil and one good. I was able to get the evil races to team up with myself, but I was unable to get the good races to team up with each other.
I would suggest that in the game creation stage you allow the player to specify more than one team. For example, give 5 teams (with the player being on team 1), which would be the most teams the game could support with 10 races (5 teams of 2). This way, I could set all the evil races to team 1, set all the good races to team 2, and have an awesome good vs. evil battle for the galaxy. Likewise I could also make 3 teams of 3, or any other combination.