The Soviet–Japanese War was a campaign of the Second World War that began with the Soviet invasion of Manchuria following the Soviet declaration of war against Japan on 8 August 1945. The Soviet Union and Mongolian People's Republic toppled the Japanese puppet states of Manchukuo in Manchuria and Mengjiang in Inner Mongolia, as well as northern Korea, Karafuto on the island of Sakhalin, and the Kuril Islands. The Soviet Union's declaration of war helped bring about the Japanese surrender and the end of World War II by undermining Japanese plans to appeal to Moscow to mediate an end to the war on favorable terms.
At the Tehran Conference in November 1943, Joseph Stalin agreed that the Soviet Union would enter the war against Japan once Germany was defeated.
An Anglo-American delegation visited Moscow in October 1944 to discuss the Soviet Union joining the war against Japan. The meeting with Stalin on 15 October discussed the Soviet Union's participation, and Stalin said that the Soviet offensive could need American material assistance because of the limited freight capacity of the Trans-Siberian Railway; see Pacific Route. British participants included Winston Churchill, Anthony Eden, Field Marshal Sir Alan Brooke, and General Hastings Ismay. The American representative was W. Averell Harriman.
At the Yalta Conference in February 1945, Stalin agreed to Allied pleas to enter World War II in the Pacific Theater within three months of the end of the war in Europe.
On 26 July, the US, the UK, and China made the Potsdam Declaration, an ultimatum calling for the Japanese surrender that if ignored would lead to their "prompt and utter destruction".
The commencement of the invasion fell between the US atomic bombings of Hiroshima on 6 August and Nagasaki on 9 August. Although Stalin had been told virtually nothing of the US and UK's atomic bomb program by Allied governments, the date of the invasion was foreshadowed by the Yalta Agreement, the date of the German surrender (on 9 May 1945, implying a deadline for Stalin to enter the war against Japan by 9 August 1945), and the fact that, on 3 August, Marshal Aleksandr Vasilevsky reported to Stalin that, if necessary, he could attack on the morning of 5 August. The timing was well-planned and enabled the Soviet Union to enter the Pacific Theater on the side of the Allies, as previously agreed, before the war's end. The proposed Soviet invasion of Hokkaido was originally planned to be part of the territory taken.
At 5 p.m. Moscow time (11 p.m. Trans-Baikal time (UTC+9)) on 8 August 1945, Soviet foreign minister Vyacheslav Molotov informed Japanese ambassador Naotake Satō in the Kremlin that the Soviet Union had declared war on Japan, and that from 9 August the Soviet Government would consider itself to be at war with Japan. At one minute past midnight Trans-Baikal time on 9 August 1945, or just over an hour after the declaration of war, the Soviets commenced their invasion simultaneously on three fronts to the east, west and north of Manchuria. The operation was subdivided into smaller operational and tactical parts:
Khingan–Mukden Offensive Operation (9 August 1945 – 2 September 1945)
Harbin–Kirin Offensive Operation (9 August 1945 – 2 September 1945)
Sungari Offensive Operation (9 August 1945 – 2 September 1945)
South Sakhalin Operation (11 August 1945 – 25 August 1945)
Soviet assault on Maoka (19 August 1945 – 22 August 1945)
Chongjin Landing Operation (13 August 1945 – 16 August 1945)
Kuril Landing Operation (18 August 1945 – 1 September 1945)
Though the battle extended beyond the traditional lands of the Manchu people, the coordinated and integrated invasions of Japan's northern territories has also been called the Battle of Manchuria. Since 1983, the operation has sometimes been called Operation August Storm, after United States Army historian Lieutenant Colonel David Glantz used this title for a paper on the subject. It has also been referred to by its Soviet name, the Manchurian Strategic Offensive Operation, but this name refers more to the Soviet invasion of Manchuria than to the whole war.
This offensive should not be confused with the Soviet–Japanese border conflicts (particularly the Battle of Khalkhin Gol of May–September 1939), that ended in Japan's defeat in 1939, and led to the Soviet–Japanese Neutrality Pact.
The Russo-Japanese War of the early 20th century resulted in a Japanese victory and the Treaty of Portsmouth by which, in conjunction with other later events including the Mukden Incident and Japanese invasion of Manchuria in September 1931, Japan eventually gained control of Korea, Manchuria and South Sakhalin. In the late 1930s were a number of Soviet-Japanese border incidents, the most significant being the Battle of Lake Khasan (Changkufeng Incident, July–August 1938) and the Battle of Khalkhin Gol (Nomonhan Incident, May–September 1939), which led to the Soviet–Japanese Neutrality Pact of April 1941. The Neutrality Pact freed up forces from the border incidents and enabled the Soviets to concentrate on their war with Germany and the Japanese to concentrate on their southern expansion into Asia and the Pacific Ocean.
With success at the Battle of Stalingrad and the eventual defeat of Germany becoming increasingly certain, the Soviet attitude to Japan changed, both publicly, with Stalin making speeches denouncing Japan, and covertly, with the Soviets building up forces and supplies in the Far East. At the Tehran Conference (November 1943), Stalin, Churchill, and Roosevelt agreed that the Soviet Union would enter the war against Japan once Germany was defeated. Stalin faced a dilemma since he wanted to avoid a two-front war at almost any cost but also wanted to extract gains in the Far East as well as Europe. The only way that Stalin could make Far Eastern gains without a two-front war would be for Germany to surrender before Japan.