Chimpanzees have been known to fight in groups and kill each other and mostly the reason is territorial disputes. Recent logging in Gabon resulted in chimpanzee warfare that resulted in the deaths of 20,000 chimpanzees.
(The Great Courses – War and World History)
I see similar issues in my neighborhood. We are seeing more deer and now a wolf has moved in because of the growth of new houses and warehouses being built where the wild animals used to live.