One more thought about this. The northeast Asian land grab by the Soviets was at the time encouraged by the US because the success of the A Bomb wasn't yet assured. The US wanted the Soviet power in the Far East as a back-up plan in case conventional arms were needed to finish the war. Therefore the US wanted the Soviets in the war, even as a Johnny Come Lately. Until they didn't, which was a rapid turn-around once the power of the bomb had been demonstrated.Of course the Soviets could've just sat back and let the US finish off Japan. But they couldn't resist the last minute east Asian land grab. Which they'd been building up to prior to the actual declaration of war on Aug 8, 45.
Of course at the time, encouragement of Soviet occupations here and there were never envisioned to be permanent.