The United States Army dropped an atomic bomb (nicknamed little boy) on Hiroshima Japan on August 6th, 1945. This bomb was the equilivant of 20,000 tons of tnt. On August 9th, the United States dropped another bomb on the city of Nagaski. This bombing was and still is to this day a controversal chapter of World War 2 history.

Effects on Hiroshima
The city of Hiroshima was of four possible selections chosen by the military for bombing. The others where Kokura, Nagasaki and Niigata. These cities were selected because they were relatively left untouched by the normal bombing of US bombers. This drop would act as a test for the bomb. At 8:15 AM the bomb was dropped over Hiroshima and missed it's target by 800 feet. The resulting mushroom cloud was an estimated 40,000 feet. Officialy, the targets in all cities where not military targets but the cities themselves, which were not military important to Japan. Out of the 90,000 buildings in the city, 60,000 were demolished. The amount of casualties was difficult to attain as many of the bomb's victims were vaporized, leaving only burnt shadows. It is now believed that 70,000 people died from the initial blast, while another 70,000 died from radiation afterwards.
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Hiroshima after the bomb

Effects on Nagasaki
The bomb dropped on Nagasaki (codenamed "Fat Man") was deemed to be alot more powerful than the one dropped on Hiroshima. However, because of Nagasaki's mountanaus terrain, alot of the bomb's devastation was prevented. Nevertheless the destruction was immense. However, Nagasaki was not the primary target for that bomb, Kokura was. But because of a heavy mist that shrouded the city, the bomber chose Nagasaki instead. It is important to note that the three day period was not offered as a time limit for the Japanese to surrender, but time required to get more plutonium for Fat Man. 70,000 people died within the first year (that number is including those who died as a result of the blast and those who died of radiation exposure.) 40% of Nagasaki was destroyed.

Reasons for the bombing
There where three main reasons why the United States chose to drop the bomb.
1. They wanted to make sure that the Japanese would surrender in order to guarantee a surrender. American casualites from the resulting attack were an estimated one million. Japanese casualites were estimated to be much higher.
2. They wanted to use the bomb before the Soviets got a chance to get involved in the war against Japan. They wanted to maintain clear military dominance.
3. The cities were remained untouched so that scientists could study the effects of the bomb to see how powerful and deadly it was.

Two days after the bomb dropped on Nagasaki, the Japanese surrendered. Supporters of the dropping of the bomb claim this saved millions of lives.

Arguments against the bombing
Although, as stated before, the US military at the time estimated that a million Americans would die in the inevitable invasion of Japan, there is no document showing where or how this number was gathered. The United States Strategic Bombing Survey (A goverment agency) conducted a detailed study of the bombing of Both Hiroshima and Nagasaki after the war. In the report, Japanese surivors and former military leaders were interviewed. The report concludes that "...Japan would have surrendered even if the atomic bombs had not been dropped, even if Russia had not entered the war, and even if no invasion had been planned or contemplated." The Japanese code was broken, and in June 1943 the allies intercepted a code quoting the emperor of Japan saying that fighting to the end was not a realistic plan. On July 13th Japan's then former minister Shigenori Togo told his ambassdor in Moscow that "Unconditional surrender is the only obstacle to peace..." The only condition on Japanese surrender was that the Emperor was to keep his place. According to American historian Martin Sherwin, this message was directed to President Truman, however it had "...no effect whatever on efforts to bring the war to a conclusion."

Legal issues
According to the 1923 Hague convention on The Rules of Aerial Warfare, it is illegal to attack cilivans or their property, or to use bombing as a way of terrorizing a people into submission. The US chose Hiroshima and Nagasaki for their "Population", which is a direct violation of this convention. Although no pilot, officer or anyone else who participated in this bombing ever stood trial for the violation or suffered any penalties whatsoever. Terrorism in the US Code of Federal regulation as “...the unlawful use of force and violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives.” (28 C.F.R. Section 0.85). Since the bombing of Hiroshima was in fact a cilivian target, and the aim was to secure a unconditional surrender from the Japanese government, this techincaly constitutes a terrorist act.
Sources
For Effects on Hiroshima, Nagasaki and the intro:
http://history1900s.about.com/od/worldwarii/a/hiroshima.htm
For Reasons for bombinbs
http://www.hiroshima-spirit.jp/en/museum/morgue_e12.html

For Arguments against the bombing
Howard Zinn;A People's history of the United States, 1492 to present. Harper Colins, New York NY. 1999. Pg.422
For Legal issues
Ward Churchill; On the Justice of Roosting Chickens: Reflections on the Consequences of U.S Imperial Arrogance and Criminality. AK Press, Oakland California. 2003.
http://www.fbi.gov/publications/terror/terror2000_2001.htm