I don't mean to be pedantic, but we're not monkeys. We're apes, and so are chimpanzees. As you linked to, communities of apes and gorillas (as well as monkeys) do fight other communities. But it's not so clear if this constitutes war. For instance, the "war" you linked to lasted for 4 years and consisted of 6 deaths.

"This “us” vs “them” outlook is also mirrored in human behavior. While the Gombe Chimpanzee War isn’t exactly identical to human war, it is strikingly similar in brutality and allegiance to a tribe." https://www.discovermagazine.com/planet-earth/a-brief-histor...

"Animal groups do compete over resources, sometimes in an organized way, but “war” implies something more formal, Dan Dembiec, supervisor of mammals at the Jacksonville Zoo and Gardens" https://www.nationalgeographic.com/animals/article/160130-an...