Divide and conquer is as old as time. Any major power usually got there by unsavoury means, making a lot of enemies along the way. The same thing happened in the US and Canada, where tribes that had fought for centuries -- quite contrary to the noble tropes, it wasn't some big love-in, and the continent was littered with raping, pillaging, slavery, and so on -- so they were more than happy to faction off to opposing sides if it gave them more of an ability to exterminate their nemesis.