If my memory serves, Stalin promised Truman that the Soviets would to go to war against Japan in three months, and they invaded Manchuria in exactly three months, to the day.
Thanks! So I was partly correct perhaps, with the Soviets wanting to spare themselves more loss. I am a bit surprised how large an offensive they were able to mount. Do you know if they had maintained a large army in the east as a defense against a possible Japanese invasion - or did they need to bring over large amounts of troops from Europe?
Stalin agreed at Yalta that after victory in Europe he would attack Japan, which agreement was reconfirmed at Potsdam.