Population size is what causes all-out war; article points out not only the behavior of ants, but humans too.
>>The reason is that societies of all species have organizational imperatives that depend on size, and only humans and certain social insects have populations that can explode into the millions. A chimpanzee community with a hundred members, for example, doesn’t address public health issues, but some ant metropolises have sanitation squads. Whether assembled largely by intelligent thought (in humans) or genetic inheritance (in ants), certain features are needed before many individuals can live together harmoniously over the long term.
The flip side is that the larger the group, the more diverse — and extreme — the aggressive responses to outsiders can be. When considering the often-striking similarities between humans and social insects, one fascinating parallel is the existence of warfare in both.<<
https://www.smithsonianmag.com/science-nature/when-it-comes-waging-war-ants-humans-have-lot-common-180972169/
