I believe that one of the constant threads in this post is the question "what is a war crime"? Since the Geneva accords weren’t developed until the 1949, the charter that empowered the winning allied nations to try the Germans, Italians, and Japanese at outset of peace established the definition.
The full charter and trial can be researched here:
http://www.law.umkc.edu/faculty/projects/ftrials/nuremberg/nuremberg.htm
The charter for the Nuremberg trials defined the following items as legal reasons to try the leadership for war related acts:
(a) Crimes against Peace: namely, planning, preparation, initiation or waging of a war of aggression, or a war in violation of international treaties, agreements or assurances, or participation in a Common Plan or Conspiracy for the accomplishment of any of the foregoing;
(b) War Crimes: namely, violations of the laws or customs of war. Such violations shall include, but not be limited to, murder, ill-treatment or deportation to slave labor or for any other purpose of civilian population of or in occupied territory, murder or ill-treatment of prisoners of war or persons on the seas, killing of hostages, plunder of public or private property, wanton destruction of cities, towns, or villages, or devastation not justified by military necessity;
(c) Crimes against Humanity: namely, murder, extermination, enslavement, deportation, and other inhumane acts committed against any civilian population, before or during the war,or persecutions on political, racial, or religious grounds in execution of or in connection with any crime within the jurisdiction of the Tribunal, whether or not in violation of domestic law of the country where perpetrated.
When it came to the destruction of London by the Germans, it fell under the clause of wanton destruction of cities, towns, or villages, or devastation not justified by military necessity.
When it came to the destruction of Hiroshima and Nagasaki, well, unfortunately the cities industrial and economic complexes were too interwoven into the city population to effectively separate them from the military necessity clause. There were actually six target cities selected by the presidential council composed of civilian and military leaders: each bombing mission had one primary and at least two secondary targets picked, in case bombing could not occur at the primary site. In the case of Nagasaki, it was actually Kobe that was the primary that day. Extensive cloud cover kept it from being bombed. Nagasaki had an immense allied POW camp, and technically shouldn’t have been considered for the primary target. If the bomb hadn’t gone off target and landed on the opposite side of the hills where it detonated, they would have had 1500 allied troops less to get back from Japan that year.
The really sad thing was that with the constant bombing of the Japanese cities with conventional explosives and incinderarys , most of the Japanese cities were burned out shells anyway. Even with this tactic, the will of the Japanese to fight had not been broken, and the suicide tactics shown at Iwo Jima and Okinawa indicated that the main assault on the mainland would be much, much worse for the allies.
A sad decision? yes. A war crime? In my opinion, no.