Which country declared war on Japan on August 8, 1945, helping accelerate Japan's surrender?

The Soviet Union declared war on Japan on August 8, 1945, helping accelerate Japan's surrender.

The Soviet declaration came late on August 8 in Moscow, which was August 9 in parts of East Asia. Soviet forces soon invaded Japanese-held Manchuria, opening a major front against Japan's Kwantung Army.

The action violated the Soviet-Japanese Neutrality Pact, which had been signed in 1941. At the Yalta Conference, the Soviet Union had secretly promised to enter the war against Japan after Germany's defeat.

The Soviet entry added pressure to Japanese leaders already confronting the atomic bombings of Hiroshima and Nagasaki. Hirohito's broadcast announcing acceptance of the Allied terms followed on August 15.