TrèsFluke"The world’s largest-known group of chimpanzees recently burst into a lethal conflict. Much like in a civil war, the group fractured into two. Then one faction began killing their former group mates on the other side... It’s an exceedingly rare event: scientists estimate that chimpanzee communities split, on average, every 500 years."
https://www.scientificamerican.com/article/two-hundred-chimpanzees-are-embroiled-in-a-civil-war/
