Democracies, it is now well established, do not go to war with each other. But they often get into wars with non-democracies. Overwhelmingly the non-democracy starts the war; nonetheless, in the vast majority of cases, it is the democratic side that wins. In other words, dictators consistently underestimate the strength of democracies, and democracies provoke war through their love of peace, which the dictators mistake for weakness.This proposition appears to be well-established only in the minds of ideologues.
It is not true empirically. World War I is a sufficient counter-example. The Boer War is another.
It is not true theoretically. Why should democracies be immune to the siren song of national insult and national aggrandizement? Why does it keep reviving, like a vampire suddenly immune to garlic?