Spite is a natural behaviour among organisms, just like mutualism and parasitism. Behaviourists define war as a loose-loose interaction in which each party is harmed by the exchange.
Among humans, war is typically fought to gain control of resources. The Nazis’ moved against the Soviet Union and waged war in North Africa primarily to gain access to the oil fields. Rome waged war in Northern Europe to gain access to wood and slaves (their energy source).
War is also an act of spite. We lose people and resources in war and in preparing for war. No one goes to war believing that they will lose. They do so thinking that the other party will suffer more damage than they will.
Resource depletion appears to be one of the significant triggers for warfare. The population hypothesis holds that wars break out when population increases exceed the ability of a territory to support that population.
Despite its intuitive appeal, the population hypothesis had not been tested. Dr. Naoko Matsumoto of Okayama University has recently provided some of the first evidence to support this theory. She studied the remains from the Jomon period of Japanese history and the Yayoi period that followed it. She found correlative data that showed that the two periods experienced different population pressures. The relatively peaceful Jomon period was largely hunter-and gathering. Their population was smaller, and they would have had more resources per person than the more violent and agrarian Yayoi.
Matsumoto’s team found a correlation between the population pressures in these two periods and the frequency of violence. However, other factors could still be behind the shift in violence.
Some of the smaller communities in the study had higher levels of violent death than the larger ones. It is unclear if these differences are due to differences in the social organization within the communities or from violence that arrived from beyond their borders.
https://www.okayama-u.ac.jp/eng/research_highlights/index_id145.html
https://www.sciencedirect.com/science/article/abs/pii/S030544032100090X