This doesn't surprise me. We've known for decades that chimpanzees groups make war on other chimpanzee groups. Eight years is a long time, though.

I think the novelty here is that this was the same group which underwent a schism of sorts, and over the course of relatively few years became two completely separate groups antagonistic to each other.

edit: I'm rate-limited, so here's my answer to your comment of:

> I remember watching a nature documentary many years ago with exactly that scenario. The original group killed all the splitters.

Yeah, you're right. You probably remember this: https://en.wikipedia.org/wiki/Gombe_Chimpanzee_War

It does seem like a very similar scenario, so now I'm confused.