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How did the Soviet declaration of war on Japan affect the Japanese government's decision to surrender?

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U.S. hydrogen bomb test in the Marshall Islands — nuclear weapon A test of a U.S. thermonuclear weapon (hydrogen bomb) at Enewetak atoll in the Marshall Islands, November 1, 1952.

The Soviet declaration of war on Japan on August 8, 1945, and the subsequent invasion of Manchuria, played a significant role in the Japanese government's decision to surrender, though historians debate the extent of its influence relative to other factors.123

Along with the atomic bombings of Hiroshima and Nagasaki, the Soviet entry into the Pacific War helped tip the scales within the Japanese government in favor of those advocating for a negotiated peace. These developments provided the necessary political momentum for peace supporters to enlist Emperor Hirohito to order a surrender.34

While some postwar investigators have argued that neither the atomic bombs nor the Soviet declaration were the sole central factors—pointing instead to the cumulative impact of the Allied naval blockade and strategic bombing—these events are widely recognized as having hastened the end of the war. Ultimately, the combination of these pressures convinced Japanese leadership of the hopelessness of continuing the conflict, leading to the formal acceptance of the Potsdam Declaration terms.1234