At 4:45 a.m., some 1.5 million German troops invade Poland all along its 1,750-mile border with German-controlled territory. Simultaneously, the German Luftwaffe bombed Polish airfields, and German warships and U-boats attacked Polish naval forces in the Baltic Sea. Nazi leader Adolf Hitler claimed the massive invasion was a defensive action, but Britain and France were not convinced. On September 3, they declared war on Germany, initiating World War II ("Germans Invade Poland").
Japanese submarines bombed the US port of Pearl Harbor in Hawaii. This bombing led the United States into World War II ("Timeline: The Road to Hiroshima").
The end of World War II was near for Europeans due to Germany's surrender (The Learning Network).
Oppenheimer led a committee which came up with a list of cities most potentially suitable as targets of atomic attacks. The committee eventually arrived at the recommendation of four targets: Kyoto, Hiroshima, Yokohama, and Kokura.
Hiroshima was chosen as the first target due to its military and industrial values. As a military target, Hiroshima was a major army base that housed the headquarters of the Japanese 5th Division and the 2nd Army Headquarters. It was also an important port in southern Japan and a communications center. The mountains surrounding Hiroshima also contributed to Hiroshima being among one of the top choices among the short list of potential targets, for that the mountains might contain the destructive forces of an atomic blast in the target area, increasing the level of destruction (Chen).
In remote New Mexico, at a site named the Trinity Test Site, the first atomic bomb was tested. The developers of the bomb had called the project the Manhattan Project. The project was headed by General Leslie R. Groves ("Timeline: The Road to Hiroshima").
The Potsdam Conference was the final war conference of the Allies. It was a meeting in Potsdam, Germany of the Big Three. The Big Three were Stalin from the Soviet Union, Churchill from Britain, and Truman from the US. President Truman had taken over presidential duties following President Roosevelt's death (Hickman). President Harry S. Truman and Prime Minister Winston Churchill demanded surrender from the Japanese ("Hiroshima Bombing").
The United States was the first country to deploy an atomic bomb in war. The bomb was dropped on Hiroshima at about 8:15 A.M. from a B-29 called Enola Gay. The bomb was nicknamed "Little Boy" (Rosenberg). The US had won the competition with Germany to create and use the first atomic weapon. The population of Hiroshima was originally marked at around 350,000. The death toll was roughly 140,000 (1945: US Drops Bomb on Hiroshima).
After Japan's refusal to surrender, the US dropped another atomic bomb, this time on Nagasaki. This bomb was nicknamed "Fat Man." It was dropped from a B-29 at approximately 11:02 A.M. Nagasaki was an important port fro Japan and the bombing caused thousands of deaths and mass destruction (1945: Atom Bomb Hits Nagasaki).
Over the radio, President Harry Truman gave a speech to address what had happened at Hiroshima three days before (The First Atomic Blast). ("American Experience").
Japan surrendered to the Allies and the second World War came to a close. It took two atomic bombs each wiping out over two-thirds a city for Japan to finally surrender (The First Atomic Blast).