On August 8, 1945, the Soviet Union officially declared war on Japan, flooding 1.6 million troops into Manchuria, an area of 600,000 square miles in the North-East of China.
Despite a strong Japanese army comprised of a million men awaiting them, the Soviet force, under command of Marshal Alexander Vasilevsky, swept into China, Korea and the Kuril Islands, forcing a rapid retreat. By the end of the engagement, the Soviets had only lost around 8,000 troops compared to the 80,000 lost by Japan.
The Soviet invasion came as a fulfilment of Stalin’s promise – made to British and American leaders at the Tehran and Yalta conferences – to join the war against Japan following the defeat of Nazi Germany. But it also came in violation of the Soviet-Japanese neutrality pact signed in 1941. The Japanese leaders had been looking to the Soviets to broker a peace with the Allied Forces in 1945, despite their public declarations of continuing to fight.
The offensive therefore came as a crushing blow to Japanese resistance, especially sandwiched as it was between the dropping of the atomic bombs on Hiroshima (Aug. 6) and Nagasaki (Aug. 9).
Devastated by American nuclear attacks and without a foothold in mainland Asia, Japanese Emperor Hirohito gave a radio address announcing an unconditional surrender on Aug. 15, which was formally signed on Sept. 2, thus ending the worst war the world had ever known.