In August 1945, the United States dropped atomic bombs at Japanese cities of Hiroshima and Nagasaki.
The BBC Climate and Science Reporter Esme Stallard explains why radiation from the blasts is undesirable.
World War in Europe ended on May 2, 1945, but the Allies, including UK, US and USSR, were fighting against Japan in East Asia.
Around 71,000 soldiers from Britain and Commonwealth died in the war against Japan, including more than 12,000 prisoners of the war, who died in Japanese captivity.
The Allies asked Japan to surrender in July 1945, but the deadline was passed.
The US dropped the first atomic bomb on Hiroshima on 6 August 1945, and the second three days later on Nagasaki. About 214,000 people were killed in the blasts and Japan surrendered.