Exactly three months after Germany's surrender, Moscow announced it would enter the Pacific War, fulfilling a secret promise made at the Yalta Conference. Soviet Foreign Minister Vyacheslav Molotov delivered the declaration to Japan's ambassador; hours later, over a million Red Army troops poured into Japanese-occupied Manchuria, hastening Japan's decision to surrender.
The timing stunned Tokyo. Japanese leaders had been quietly hoping Moscow might broker a negotiated peace with the Allies, unaware that Stalin had already committed at Yalta to join the war against Japan within three months of Germany's defeat—a pledge he fulfilled to the day.
Molotov summoned Japanese Ambassador Naotake Satō to the Kremlin and read the declaration aloud just before midnight Moscow time. Within hours, three Soviet fronts comprising over 1.5 million soldiers, thousands of tanks, and combat aircraft surged into Manchuria in Operation August Storm, overwhelming Japan's depleted Kwantung Army.
The declaration landed on the same day Nagasaki would be bombed and compounded the shock already reverberating from Hiroshima two days earlier. For Japan's leadership, the combination of a second atomic weapon and the collapse of any hope for Soviet mediation proved decisive, accelerating the surrender deliberations that concluded within a week.
Key people: Joseph Stalin, Vyacheslav Molotov