Arguably fighting against Japan and Germany in WW2 is one of the only times the US used their military in a justifiable way. Fascism had to be stopped.

The Japanese military expected to lose 20 million people in the very first battle of the invasion, and the Americans were considering using poison gas because the casualties of fighting it out in the streets would have been in the millions of troops. People don't realize how dark it was in 1945, food shipments had all but ceased, Japan was entering a famine; if the war had dragged on through a land invasion it would have been cataclysmic.