When did the Operation that seized the territories formally claimed by  Manchukuo began
Manchukuo:  The territories formally claimed by the puppet state were first seized in the Soviet invasion of Manchuria in August 1945, and then formally transferred to Chinese administration in the following year. Soviet invasion of Manchuria: The Soviet invasion of Manchuria, also known as the Manchurian Strategic Offensive Operation ("Манчжурская стратегическая наступательная операция" , lit. Soviet invasion of Manchuria:  "Manchzhurskaya Strategicheskaya Nastupatelnaya Operaciya") or simply the Manchurian Operation ("Маньчжурская операция"), began on 9 August 1945 with the Soviet invasion of the Japanese puppet state of Manchukuo.
9 August 1945