Sometimes "1+1" does not equal 2. When the two greatly contradictory interest groups separated, their chances to undermine each other decreased, which allowed them to play a bigger role on the battlefield instead.
What came next was all about protecting their own interests, and they would certainly put all their effort into it. Even if the Warhammer Kingdom fell, many Noble Castles would still stand firm.
Ancient tribes is a general term, and only they themselves can understand how many species are actually included internally.
With more people come more problems, let alone a multi-species Alliance. At this moment, when they're fighting to conquer, they can struggle together for shared interests, but once there are results, that's when things start to break apart.
Not every species harbors grand ambitions. Most of the ancient tribes just want a piece of land suitable for survival, and those vying for continental supremacy are almost non-existent.
