As societies modernize, they become less dependent on local agricultural output

The Climate Wars Myth by Dr. Bruno Tertrais.

Since the dawn of civilization, warmer eras have meant fewer wars. The reason is simple: all things being equal, a colder climate meant reduced crops, more famine and instability.4 Research by climate historians shows a clear correlation between increased warfare and cold periods.5 They are particularly clear in Asia and Europe, as well as in Africa.6 Interestingly, the correlation has been diminishing since the beginning of the Industrial Revolution: as societies modernize, they become less dependent on local agricultural output.7