How Did War Help Build Civilization?

David Geary says war was the primary driver of the building of civilizations. Once groups compete, larger coalitions have the advantage. Nomadic raiders invading agricultural communities was a common dynamic before empires. The farming communities unite and start building defenses. The nomads then have to unite into larger, better organized groups to stay competitive. Both sides ramp up and develop new technology. As societies expand, not every man can serve in the military. Someone has to make weapons, bring in the harvest, and run markets, so the economy diversifies. The stress that produced the large groups, he says, was competition between groups.

He calls intense cooperation and intense conflict two sides of the same coin. People are intensely cooperative, including among non-relatives: large cities, layered societies, a drive down the street, a shopping center where a person is safe, and different people doing different work. Most cooperation in other species is among kin. The benefit he sees in large-group cooperation is defense or offense against other groups. The competition does not need to stay violent. It can later turn into trade wars or other contests between groups. Violence, in his argument, was the initial driver, and more of it meant more push toward large-scale cooperation.