This isn’t a new idea, but its irony makes it interesting. As Revenge: What is it good for? points out, warfare grows out of our ability to cooperate:
“Humans developed the ability to model actions before they happen. This means we can plan collective violence. It explains why we have warfare,” Dr. Roscoe says. Research on chimps confirms that once you can gang up and launch a surprise attack on outnumbered victims, killing becomes a dramatically more attractive option.
If every fight’s one on one, the odds are rarely strongly on your side. Once you can gang up on enemies though, you can expect to win with only minor losses.