Relations between the North and the South had been chilly for years, but a wise old diplomat kept the factions united until time caught up with him. In the power vacuum following his death, the kingdom split in two—an ambitious young king in the North battling two young pretenders in the South. After a relentlessly brutal four-year campaign of open warfare, intimidation, and assassination, the North rose, the South fell, and the fractured and war-weary kingdom was finally united once more.
As you probably guessed from the headline, I'm not talking about humans—I'm talking about the chimpanzees of the Gombe Stream National Park in Tanzania, famously studied by Jane Goodall in the late 1960s and early 1970s. Goodall discusses chimpanzee intercommunity conflict, and what it says about our shared capacity for intergroup violence, in this clip from a 1997 interview:
Researchers at Duke University, armed with Goodall's meticulously detailed journals and new social networking analysis tools, have been able to reconstruct the timeline of this conflict—the only documented chimpanzee war (but almost certainly not the only chimpanzee war)—in unprecedented detail. What they've found is that chimpanzee factions emerged in much the same way human factions emerge in similar conflicts, and on a similar timeline: increasing social segregation and small-scale conflict can become full-scale war when social power falls away from peacemakers and ends up in the hands of more ambitious, dominant personalities.
Fortunately, chimpanzees are less habitually violent than humans. As the New Scientist article on the study notes, DNA analysis tells us that chimpanzee communities can go for entire centuries without war.