HOW UGANDA'S LARGEST WILD CHIMPANZEE COMMUNITY SPLINTERED INTO A DEADLY CIVIL WAR

Fort Worth Star-Telegram

 

How Uganda’s Largest Wild Chimpanzee Community Splintered Into a Deadly Civil War

By Ryan Brennan

April 10, 2026 1:30 PM

 

For decades, the Ngogo chimpanzees in Uganda’s Kibale National Park were the largest known wild chimpanzee community — nearly 200 individuals living, grooming, hunting and patrolling together as one society.

 

Then, slowly and then suddenly, they turned on each other.

 

What followed was a years-long civil war that left dozens dead and split the community in two.

 

Scientists say permanent chimpanzee community fissions are exceedingly rare — genetic evidence suggests they happen roughly once every 500 years. Researchers happened to be watching when this one occurred.

 

Their findings were published in the journal Science on April 9.

 

The Chimpanzees Were Once Unified and Friendly

 

Researchers began tracking the Ngogo group in 1995, when the community numbered over 100.

 

Over the following years, it swelled to nearly 200 individuals, including more than 30 adult males — possibly straining the group’s capacity to maintain relationships.

 

Social ties clustered around three groups: Western, Central and Eastern. Despite that clustering, the chimps functioned as one community. They shared territory, mated across clusters and conducted joint border patrols and hunts.

 

Highly respected individuals served as “social bridges” connecting the cliques.

 

Then, in 2014, five adult males died, likely from disease. Several of them were key social bridges — and their loss weakened the connective tissue holding the community together.

 

A new alpha male was crowned around the same time, adding to the tension that eventually led to a civil war.

 

The Moment ‘All Hell Broke Loose’

 

On June 24, 2015, researcher Aaron Sandel was observing the Ngogo chimps when a Western party approached a Central party near the center of their shared territory.

 

Instead of mingling as usual, the Western chimps fell silent and fled. The Central chimps chased them.

 

An unprecedented six-week period of avoidance followed. John Mitani, with two decades of chimp research, was stunned. It was during that period that “all hell broke loose,” Mitani recalled, per the New York Times.

 

From there, the Western and Central clusters interacted less and less. Mating occurred only within each cluster. By 2017, the two groups held entirely separate territories, and the former center of the community became a patrolled border.

 

That same year, Western chimps attacked and severely injured the alpha male of the Central cluster.

 

The Civil War Turns Violent — and Deadly

 

By 2018, the split became permanent — socially, spatially and reproductively. Females and offspring would no longer even feed at the same fig tree.

 

The violence was devastating. Western chimps killed seven adult males and 17 infants from the Central cluster. 14 more Central males disappeared without a trace, likely also killed.

 

In 2021, the violence escalated to infanticide, with 14 Central infants stolen and killed. Among the named victims was Basie, a 36-year-old Central male who was encircled and killed in 2019.

 

At least two more attacks have been documented since data analysis ended in 2024.

 

What Caused the Chimpanzee Civil War?

 

The researchers theorized that social relationships broke down under multiple pressures.

 

Suspected stressors included the unusually large group size straining relationship maintenance, competition over food and reproduction, alpha male turnover amplifying tensions and disease deaths removing key social bridges.

 

Within any chimp group, violence flares occasionally — but it is usually dampened by long friendships. When the bridges fell, there was nothing left to contain it.

 

The Ngogo split was not entirely without precedent.

 

Jane Goodall observed something similar in Gombe, Tanzania, in the 1970s — a four-year lethal split among about two dozen chimps. Critics dismissed it as an artifact of Goodall feeding the chimps bananas.

 

Ngogo confirms it wasn’t a fluke. Sandel said this is “the first time that you could say definitively that the civil war is actually happening.”

 

The Gombe split was preceded by the same warning signs: clustering, reproductive competition, alpha male changes and deaths of bridging males.

 

A community of 200 didn’t collapse because of any single dramatic event. It collapsed because the quiet, invisible scaffolding of friendships gave way — one death, one missed grooming session, one avoided encounter at a time.

 

The Ngogo story is a reminder that even among our closest living relatives, the bonds that hold a society together can be far more fragile than they appear.