Russia's Invasion Plans: The Atomic Bomb's Impact

The Soviet Union's invasion of Manchuria and Sakhalin Island on 9 August 1945, and not Russia's invasion of Japan, was one of the factors that led to Japan's surrender in World War II, along with the atomic bombings of Hiroshima and Nagasaki by the United States on 6 and 9 August 1945, respectively.

The Potsdam Declaration

Two months after Germany surrendered, Allied leaders gathered in Potsdam, Germany, to discuss peace settlements, among other issues. However, although the European phase of the conflict had ended, the war continued in the Pacific theatre as Japan remained committed to fighting. U.S. President Harry S. Truman, British Prime Minister Winston Churchill, and Chinese Nationalist leader Chiang Kai-shek thus drafted a declaration that defined the terms for Japan's surrender and made dire warnings if the country failed to put down its weapons.

The declaration claimed that “unintelligent calculations” by Japan’s military advisers had brought the country to the “threshold of annihilation.” The leaders hoped that the Japanese would “follow the path of reason” and outlined their terms of surrender, which included complete disarmament, occupation of certain areas, and the creation of a “responsible government.” The declaration also promised that Japan would not “be enslaved as a race or destroyed as a nation.” It ended by warning of “prompt and utter destruction” if Japan failed to unconditionally surrender.

At a press conference, the Japanese Prime Minister Suzuki Kantarō responded to the ultimatum with “mokusatsu,” which can be translated as "killing with silence." While the press largely reported that he was refusing or ignoring the declaration, others later noted that mokusatsu could also mean “no comment.”

On August 6, 1945, the U.S. military dropped an atomic bomb on Hiroshima, Japan, destroying most of the city. More destruction followed as Nagasaki was bombed three days later. During this time, the Soviet Union also declared war on Japan and invaded Manchuria on three fronts. On August 14, the Japanese government sent a letter of surrender. The next day, Emperor Hirohito announced his country's unconditional surrender in a radio address. The formal surrender ceremony took place on September 2, 1945, aboard the USS Missouri in Tokyo Bay.

The Manhattan Project

The project was also responsible for gathering intelligence on the German nuclear weapons project and served in Europe, sometimes behind enemy lines, to gather nuclear materials and documents and round up German scientists. Despite the Manhattan Project's emphasis on security, Soviet atomic spies penetrated the program.

The first nuclear device ever detonated was an implosion-type bomb during the Trinity test, conducted in New Mexico on July 16, 1945. The Little Boy and Fat Man bombs were used a month later in the atomic bombings of Hiroshima and Nagasaki, respectively.

The Soviet-Japanese Neutrality Pact

The pact was signed two years after the conclusion of the Soviet-Japanese Border War and was intended to safeguard the eastern border of the Soviet Union and concentrate on the European Theatre of World War II. For the Empire of Japan, the pact was intended to secure the northern border of Manchukuo from a possible Soviet invasion.

The pact proved beneficial for both countries. The assurance of Soviet neutrality encouraged Japan towards Southern expansion and the invasion of the European colonies in Southeast Asia. Likewise, the absence of a Japanese threat enabled the Soviets to move large forces from their Far East region and concentrate them on the European theatre of war.

In 1945, the Soviet Union scrapped the pact and joined the Allied campaign against Japan. On August 9, 1945, the Soviets invaded Manchuria, and a declaration of war against Japan followed six hours later. This invasion, along with the atomic bombings of Hiroshima and Nagasaki, led to Japan's surrender and the end of World War II.

The Instrument of Surrender

The signing took place on the deck of the USS Missouri in Tokyo Bay on 2 September 1945. The ceremony lasted 23 minutes and was broadcast around the world. The instrument was first signed by the Japanese foreign minister, Mamoru Shigemitsu, "By Command and on behalf of the Emperor of Japan and the Japanese Government". General Yoshijirō Umezu, Chief of the Army General Staff, then signed the document "By Command and on behalf of the Japanese Imperial General Headquarters".

US General of the Army Douglas MacArthur, the Commander in the Southwest Pacific and Supreme Commander for the Allied Powers, accepted the surrender on behalf of the Allied Powers and signed in his capacity as Supreme Commander. After MacArthur, the following representatives signed the instrument of surrender on behalf of each of the Allied Powers:

• Fleet Admiral Chester Nimitz for the United States
• General Xu/Hsu Yongchang for China
• Admiral Sir Bruce Fraser for the United Kingdom
• Lieutenant General Kuzma Derevyanko for the Soviet Union
• General Sir Thomas Blamey for Australia
• Colonel Lawrence Moore Cosgrave for Canada
• Général de Corps d'Armée Philippe Leclerc de Hauteclocque for France
• Lieutenant Admiral Conrad Helfrich for the Netherlands
• Air Vice-Marshal Leonard M. Isitt for New Zealand

The Pacific War

The Allies adopted a Europe-first stance, giving first priority to defeating Nazi Germany. The Japanese had great difficulty replacing their losses in ships and aircraft, while American factories and shipyards produced ever-increasing numbers of both. The Allies' island-hopping strategy saw them gradually drive back the Japanese. Fighting included some of the largest naval battles in history and massive Allied air raids over Japan.

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