Absent a second war in Europe, would the Soviets have intervened in the second Sino-Japanese War?
Stalin was a cautious fellow, but considering how easily the Soviets defeated Japan at Khalkin Gol it seems like it'd be a safe move for the USSR to drive the Japanese from the mainland. They'd gain Manchuria and Korea as satellites and the most they could lose to Japan is northern Sakhalin (where Japan was mostly benefitting from the oil anyway IIRC).