Sure, there’s always the option to go to war, but it’s painfully obvious in the early stages of the game that going to war is expensive, and anyone in a fight is going to set themselves way behind the noncombatants in the resource chase, which just lets the peacemongers run away with the game. After someone picks a single fight, they’re so resource-constrained that they’ll get hammered in their next fight trying to drag someone else down.
To be fair, this is a problem that has plagued a fair number of computer 4x games over the years as well. It seems to be an issue that's difficult to balance properly.