Ever heard of Smedley Darlington Butler?
How about "Devil Dogs"?
Butler was, at least during his lifetime, the most decorated solder in U.S. military history. To this day, not very many have won TWO Medals of Honor. Then, after a thirty-three year career of exemplar service to this country, Butler experienced an enlightenment. He began a campaign against war.
War Is A Racket is his book explaining his position, how he arrived at that position, and his recommendation for dealing with war. Here is my review of that book.