Neighbors Turned Killers: The Chimpanzee Civil War

The largest-known group of wild chimpanzees has split in two. Two hundred chimps in Uganda's Kibale National Park — once a single unified community — have divided into warring factions, one side waging a multi-year campaign of lethal strikes against the other. The part that keeps scientists up at night: these were not strangers.

Researchers have tracked the Ngogo population for thirty years, and what they witnessed was a fracture playing out at a snail's pace. Starting around 2015, the group began pulling apart. Alliances collapsed, subgroups hardened, and shared territory became a front line. The split was complete by 2018.

Between 2018 and 2024, researchers witnessed Western adults kill seven males and 17 infants from the Central group. Killing rates far exceeded those estimated for intergroup aggression among chimpanzees generally, and there may have been more. Over those years, more than a dozen Ngogo Central chimps died under unknown circumstances. Apparently healthy primates would simply disappear, their bodies never recovered.

Researchers hypothesize that deaths of several chimps in 2014, a 2015 change in the alpha male and a respiratory epidemic in 2017 had led social ties to weaken and the group to splinter. The same general sequence preceded Jane Goodall's "Four-Year War" at Gombe in the 1970s, the only prior documented case, though because Gombe chimpanzees frequently ate bananas provided by humans, some primatologists doubted whether that fission was natural behavior. Ngogo, researchers say, is the first time you can call it definitively a civil war.

Because chimpanzees lack cultural markers like religion or ethnicity, the authors argue that studying them could illuminate the role of relational dynamics in human warfare. No ideology required. Just fraying social bonds and someone deciding a former grooming partner is now the enemy.

Scientists estimate this kind of conflict occurs only once every 500 years. We happened to be watching.

Read the full story at BBC Science Focus

Hot Take: The part of this story that should sit with people is not that chimps can go to war — it's that they do it without religion, ethnicity, or any of the frameworks humans use to explain why neighbors turn on neighbors. The Ngogo data makes a clean, uncomfortable argument: sometimes all it takes is losing the right few individuals who were holding things together.