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By August 1945, U.S. and British Commonwealth forces had pushed the Japanese back through Southeast Asia to the Japanese mainland, while Japanese control in China was weakening each day, and the Soviet Union was rapidly approaching from the west. However, despite inevitable defeat looming over the Empire of Japan, its military leaders encouraged its forces to fight to the death, and Japanese resistance grew in ferocity as they were pushed back to the mainland, most notably on the islands of Iwo Jima and Okinawa. As U.S. leadership realized that an amphibious assault on the Japanese mainland would result in heavy and unnecessary casualties on both sides, including large numbers of civilians, an alternative measure was sought. The USSR's advance also put time pressure on the Americans, as defeating Japan quickly would give the U.S. more time to assert control over the region, without having to split control with the Soviets (as was the case in Germany).

The bombs are dropped

On May 31, 1945, it was suggested that the U.S. demonstrate the power of the atomic bomb to the Japanese, to convince them to surrender - the plan was rejected, however, in the fear that it was not convincing enough, that the Japanese may shoot down the plane, or that the bomb was a dud - instead, a surprise attack was viewed as the most effective course of action. Following the Trinity Test in July 16, the United States achieved the goal of successfully creating and detonating a nuclear weapon. On July 26, the leaders of the U.S., UK, and China all called for the unconditional surrender of Japan, otherwise Japan would face "prompt and utter destruction". Japan did not surrender, and on the morning of August 6, the Enola Gay B-29 bomber dropped an atomic bomb, known as "Little Boy", over the city of Hiroshima. Japan still refused to surrender, and three days later, another bomb, known as "Fat Man", was dropped over Nagasaki. Japan's surrender was announced on August 15, and formalized on September 2, 1945, bringing WWII to a close.

Impact

The bomb dropped over Hiroshima was a uranium 235 bomb, which detonated at approximately 580 meters (1,900ft) above the ground and had a yield of 16 kilotons (i.e. it had the same blast force as 16,000 tons of TNT). The bomb dropped over Nagasaki was a plutonium 239 bomb, which detonated at approximately 500 meters (1,650ft) and had a yield of 21 kilotons. The temperatures at the epicenter of the explosions reached around 3,000-4,000 degrees Celsius, and thermal radiation was so strong that it caused third degree burns over a kilometer from ground zero. The majority of those within a one km radius of both explosions were killed instantly through the blast force and intense heat, while those further away were more susceptible to injuries by burning, falling debris and glass, and radiation. Additionally, as the fallout from the blast (i.e. radioactive dust and ash sent into the air by the explosion) returned to the ground it was carried by the wind to populations outside of the blast radius, and radiation sickness then took hold over the days and weeks that followed. Due to the nature of the attack, Japan's population distribution at the time, and the long-term effects of radiation poisoning (which may be responsible for illnesses and death several years after exposure), there is no accepted consensus on the total number of deaths due to the atomic bombings at Hiroshima and Nagasaki -the figures given appear to be on the lower end of estimate ranges, where combined estimates generally vary between 110,000 and 210,000 deaths.