It was the Law. All the tribes fought to get to Nirvana. Once all the tribes were defeated the gates at the top of the temple would open and everyone who survived would be able to pass, but it didn't turn out that way.

It's a long story, and I don't really remember everything that happened right at the end, but the last thing I know is that me and me comrades were trying to reach the gate and everything falling apart around us.