Examining Russia's WW II Japan Offensive

Did Japan surrender in 1945 because of the death and devastation caused by the atomic bombs dropped by the Americans on Hiroshima and Nagasaki or because of the crushing defeat inflicted on their armies by the Soviet Union in Manchukuo, the puppet state they set up in north-east China? Indeed, the Red Army’s rapid and total victory in Manchukuo has been relatively neglected by historians.