I found this quote from historian Howard Zinn insightful:
There is a persistent argument against such a possibility, which I have heard from people on all parts of the political spectrum: We will never do away with war because it comes out of human nature. The most compelling counter to that claim is in history: We don’t find people spontaneously rushing to make war on others. What we find, rather, is that governments must make the most strenuous efforts to mobilize populations for war. They must entice soldiers with promises of money, education, must hold out to young people whose chances in life look very poor that here is an opportunity to attain respect and status. And if those enticements don’t work, governments must use coercion: They must conscript young people, force them into military service, threaten them with prison if they do not comply.
He follows up with assorted examples.