We just had this problem in a game. Started Greece as a group, and there were a couple of big civs. Mongolia were attacking people but for no actual reason/benefit, and Rome were taking all the wonders.
Anyway, we got a couple of tech victories and won a war, and suddenly our civ is full of people jumping in from all over, including the King of Mongolia who was like, "well, NOW we can start playing the game properly".
So we made sure one team member had Masonry as the MVP and jumped ship to a new nation.