Is bombing justifiable?

In the right state of mind bombing will never be justifiable, but when a country is at war it is all they can do to win. During world war 2 when America was at war with japan, America bombed two major japanese cities killing millions and damaging future generations with the effects of radiation. However it is not justifiable to go around killing millions for the sole purpose to rid the earth of them. I believe that bombing a country to protect your own citizens is a justifiable act. I also believe that bombing or killing citizens because you don't like them, and not even to win the war is not a justifiable act.