While it was horrible that civilians were killed, we must remember that the emperor ordered ALL the civilians of japan to resist invaders to the last man, woman and child, so you could technically consider them enemy combatants. Also, the effects of the A-bomb were/are horrible on any survivors but let's remember that the use of that bomb saved millions of lives, including millions of japanese lives. Like Cyanista said too, they weren't dropped for revenge, all America wanted was for the war to be over.