The Metrons are just a powerful race that forced two less powerful races to get along.
Actually the Metrons did nothing of the kind. They merely provided an arena (hey, there's a catchy word for it!) to allow representatives of those two races to work out their own conflict, one way or the other. The Metrons even claimed they'd destroy the ship of the loser, so as to give both captains incentive to fight. Hardly forcing them to get along -- rather the opposite, I'd say. (Though personally I've always believed they actually would've destroyed the winner's ship as the greater threat.)