6 August 1945
On August 6 and 9, 1945, the cities of Hiroshima and Nagasaki, Japan, were totally destroyed by the first atomic bombs used in warfare. The American government justified the use of the bombs by saying that they wanted to shorten the war. The bomb dropped on Hiroshima killed as many as 140,000 people, while the one dropped on Nagasaki killed as many as 90,000 people. People continued to die even after the bombings, due to secondary illnesses (for example, cancers) caused by the immense radiation. In both cities, the majority of the dead were civilians. The bombing forced the Japanese to surrender to the Allied forces. The atomic bombing of Hiroshima, along with that of Nagasaki on August 9, is to date the only attack with nuclear weapons in the history of warfare. Six days after the bombing of Nagasaki, 15 August, Japan surrendered to the Allied Powers, ending World War II. The end of the war and introduction of the atomic bomb plus the scramble by the big powers to carve out spheres of influence led to the heightening of tension and the beginning of the Cold War.
References

Rosenberg,J.,'The Atomic Bombing of Hiroshima and Nagasaki' ,from about.com,[online], available at www.about.com [Accessed: 02 August 2013]|

history, 'The Bombing of Hiroshima and Nagasaki' from history',from history, [Online], Available at www.history.com [Accessed: 02 August 2013]