Which 1945 Soviet military campaign began just before the atomic bombing of Nagasaki?

The Soviet invasion of Manchuria began on 9 August 1945, just before the atomic bombing of Nagasaki.

Soviet forces attacked Japanese-held Manchuria and the Japanese puppet state of Manchukuo. The campaign is also known as the Manchurian Strategic Offensive Operation and, in some Western accounts, Operation August Storm. Soviet troops crossed into the region after the Soviet Union declared war on Japan, honoring commitments made to the other Allied powers.

The timing was dramatic: Hiroshima had been bombed on 6 August, the Soviet declaration and invasion began on 9 August, and Nagasaki was bombed later that same day. Soviet forces rapidly defeated the Kwantung Army, Japan’s main force in Manchuria, and occupied large areas of Northeast Asia.

Historians continue to debate how Japan weighed the Soviet attack against the atomic bombings when deciding to surrender. The invasion clearly destroyed Japanese hopes that Moscow might mediate a favorable peace and added a powerful military threat to the crisis facing Japanese leaders.