1945

Soviet–Japanese War

Soviet Union declares war on Japan

Japan's ambassador called on Molotov still hoping Moscow might mediate a peace. Molotov handed him a declaration of war that took effect “tomorrow” — about an hour away in the Soviet Far East.

5 p.m. in Moscow

At 5:00 p.m. Moscow time on 8 August 1945, Soviet foreign commissar Vyacheslav Molotov received the Japanese ambassador Naotake Satō and handed him the Soviet government's declaration.

It cited Japan's rejection of the Potsdam demand, refused Japan's request for Soviet mediation, and announced Soviet adherence to the Allied demand for surrender.

Satō's attempt to warn Tokyo directly was frustrated, and Japanese leaders learned of the declaration only as the invasion was beginning.

“From tomorrow”

The operative language said the Soviet government would consider itself at war with Japan from the following day, 9 August. The announcement was broadcast at about 10:00 p.m. Moscow time; a contemporary U.S. diplomatic memorandum noted this gave Japan roughly two hours' notice by Moscow reckoning.

Shortly after midnight on 9 August in the Soviet Far East, advance Soviet forces crossed into Japanese-controlled Manchuria. Accounts give the first crossings variously as just after midnight, 12:01 a.m. or about 12:10 a.m. — an exact minute is not recoverable across so vast a theatre.

Three fronts had been ordered against Japanese forces: the Trans-Baikal, 1st Far Eastern and 2nd Far Eastern, under Aleksandr Vasilevsky.

The mediator becomes a belligerent

The USSR was fulfilling Stalin's secret Yalta commitment to enter the war two or three months after Germany's surrender, while pursuing its own strategic and territorial objectives.

Japan's immediate loss was the neutral power it had hoped might broker an end to the war; the destruction of the Kwantung Army and the occupation of territories came later, and operations against South Sakhalin and the Kurils were separately organized on later dates.

Historians continue to weigh Soviet entry against Hiroshima, Nagasaki, blockade and Japan's military position in explaining the surrender; no single exclusive cause is established.

Sources

Researched 24 Aug 2026 9 sources not yet audited Date corrected

How this was checked

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Date corrected. The research places this at 1945-08-08.

What the sources leave uncertain

August 8 is the secure date on which Molotov delivered and Moscow broadcast the declaration. The document itself made the state of war effective August 9, which was already close at hand in the Soviet Far East and Japan.
Sources describe the first border crossings as shortly after midnight, 12:01 a.m., or about 12:10 a.m. Far Eastern time. The exact minute should not be treated as certain across the enormous theater.
Historians continue to debate the relative weight of Soviet entry, Hiroshima, Nagasaki, blockade, conventional bombing, and Japan’s military situation in producing surrender. The declaration’s importance is clear, but a single exclusive cause is not established.