The Regulars: The American Army, 1898-1941 by Edward M. Coffman
In 1898, the American Regular Army was a small frontier constabulary engaged in skirmishes with Indians and protesting workers. Forty-three years later, in 1941, it was a large modern army ready to wage global war against the Germans and the Japanese. In this definitive social history of America's standing army, military historian Edward Coffman tells how that critical transformation was accomplished.