Researchers have documented what appears to be the first recorded instance of "civil war" among wild chimpanzees.
The study, published in the journal Science, details how the Ngogo chimpa community in Uganda's Kibale national park fractured into two hostile factions between 2015 and 2018.
Primatologist Aaron Sandel first noticed warning signs in June 2015 whilst observing a small group of the Ngogo chimps.
When other members of the broader community approached through the forest, the chimpanzees he was watching became visibly anxious.
They grimaced and sought physical contact with one another for comfort, behaving as though encountering strangers rather than familiar companions.
Mr Sandel said: "Cases where neighbours are killing neighbours is more troubling and, in a way, it gets closer to the human condition.
"How do we have this seeming contradiction within us where we are able to cooperate, but then also very quickly turn on one another?
"These shifting group identities and dynamics that we see in human civil war rarely have a parallel in other animals, but they do have a parallel in the case of chimpanzees."
Mr Sandel spotted warning signs in June 2015 whilst observing a small group of the Ngogo chimps
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The research team analysed over 30 years of behavioural data from what constitutes the world's largest documented wild chimpanzee population.
From 1995 until 2015, the community had remained socially unified, but internal dynamics then started changing.
By 2018, two separate groups had formed - the western chimps and the central chimps.
Following this permanent division, the western faction launched 24 coordinated and sustained assaults against the central group over a seven-year campaign.
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The Ngogo chimpanzee community in Uganda's Kibale national park fractured into two hostile factions
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These attacks resulted in the deaths of at least seven adult males and 17 infants.
The deaths of several influential older individuals in preceding years destabilised the community's social fabric, researchers believe.
Mr Sandel said: "Their abrupt death likely weakened connections among the neighbourhoods, which then made the group vulnerable to this polarisation that happened when the alpha change occurred.
"Then there was also a disease outbreak in 2017 that probably made the split inevitable, or expedited it slightly."
The attacks resulted in the deaths of at least seven adult males and 17 infants
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However, human activities that undermine social bonds - including deforestation and disease outbreaks - could increase the frequency of these devastating inter-group wars, Mr Sandel warned.
Brian Wood, an evolutionary anthropologist at the University of California Los Angeles who has previously researched the Ngogo chimps but did not participate in this study, emphasised the evolutionary logic behind such violence.
He said: "You can increase your Darwinian fitness by increasing your own survival, increasing your reproduction or by decreasing the survival and reproduction of your competitors.
"And this is what the western chimps have done. The central chimps, after facing the onslaught of the westerners, now have the lowest survivorship that has ever been documented in a wild chimpanzee community."
Sylvain Lemoine, a biological anthropology professor at the University of Cambridge, described the research as groundbreaking.
"Here we have the first thoroughly reported case of what can be qualified as civil warfare in the species," Prof Lemoine said.