The Second World War is believed to have claimed the highest number of lives in the human history. The controversy in it was that in spite of it being the bloodiest war ever for soldiers, more civilians were killed than soldiers. The setting of the Second World War purposefully and intentionally targeted the heavily populated areas with an aim of killing more civilians.
One of the reasons claimed for the attack of civilians was to create fear and demoralize them so that they can rise against their government by not supporting it and probably it this would force it pull out of the war. Maximum damage to a countries population would mean that the country had been beaten up and rendered weak to resist. The civilians were expected to force their respective governments to withdraw from the war than to endure more suffering. In addition to this, it was assumed that the real effect of war could be well felt if the civilians were attacked. This was seen as a good way of keeping up for the fight. Another reason why the civilians were targeted during the Second World War was purely ideological. A good example was the attack of the Jews civilians by the Germans.
The United States bombing campaign that culminated in dropping the atomic bombs in Japan is justifiable. Dropping these bombs, especially the atomic bomb in Hiroshima and Nagasaki in Japan prompted the end of the World War II, shortening a war which would otherwise have been prolonged and claim lives of many innocent civilians. Still, based on the fact that preparing and conducting military attacks was costly, then one can judge reasonably that it was far much better for America to use the atomic bomb than to bomb Japan and end the war forthwith. Military attacks would have not only prolonged the war but also be more costly and claim many solders and civilian lives.