Smedley Butler wrote War is a Racket in 1935. An excerpt from Wikipedia:

War is a racket. It always has been. It is possibly the oldest, easily the most profitable, surely the most vicious. It is the only one international in scope. It is the only one in which the profits are reckoned in dollars and the losses in lives. A racket is best described, I believe, as something that is not what it seems to the majority of the people. Only a small 'inside' group knows what it is about. It is conducted for the benefit of the very few, at the expense of the very many. Out of war a few people make huge fortunes.

Butler confesses that during his decades of service in the United States Marine Corps:

I helped make Mexico, especially Tampico, safe for American oil interests in 1914. I helped make Haiti and Cuba a decent place for the National City Bank boys to collect revenues in. I helped in the raping of half a dozen Central American republics for the benefits of Wall Street. The record of racketeering is long. I helped purify Nicaragua for the international banking house of Brown Brothers in 1909-1912 (where have I heard that name before?). I brought light to the Dominican Republic for American sugar interests in 1916. In China I helped see to it that Standard Oil went its way unmolested.