This is a tough one.

Although Germany started the bombing of civilians in both wars, it was soon two way traffic.

But was it legal under international law, should it matter if it was or not?

Early R.A.F. attempts at pin point bombing failed, and 'Bomber' Harris soon had 'area' bombing in full swing.

The United States began its strategic bombing campaign by legal (according to international law) daylight "precision bombing" of military targets in or around urban areas. In Europe, its loss of bombers became such that it adopted the British strategy of nighttime, indiscriminate urban bombing. For Japan, precision bombing was the rule until the above mentioned General LeMay took over the 20th and 21st bomber Commands, and initiated the firebombing of Japanese cities, he thought the Japanese deserved it.

R.J. Rummel on.......
http://www.hawaii.edu/powerkills/COMM.10.5.03.HTM

says was the indiscriminate (meaning the target was the city, usually the city center, and not military installations) American bombing of urban areas democide (mass murder), that is, the intentional targeting of unarmed civilians with deadly weapons? I don't see how this can be denied. Bombs were dropped intentionally on unarmed civilians in their homes or at work. These people died not because they lived near military targets or were caught in the crossfire of battle, but because of their nationality and the urban area in which they lived. It was democide. I think LeMay was correct. Not only would he, McNamara, and others on his planning staff, be charged with war crimes had the Japanese won, but in fact they had committed war crimes.

Or do you do anything to win a war once your in it?

“War is a nasty, dirty, rotten business. It’s all right for the Navy to blockade a city, to starve the inhabitants to death. But there is something wrong, not nice, about bombing that city.” – Marshal of the Royal Air Force, Sir Arthur “Bomber” Harris