War is a billionaire’s extortion racket, baptized in the blood of impoverished teenagers.

Smedley Butler (1881–1940) American Marine Corps officer, war hero, anti-war activist

(Spurious)

Widely circulated in social media, this is less of a quote than a paraphrase of various anti-war statements Butler made, including in his book War Is a Racket (1935), itself an expansion of a lecture series by Butler in the early 1930s.