Based on a detailed investigation of all the facts, and supported by the testimony of the surviving Japanese leaders involved, it is the Survey’s opinion that certainly prior to 31 December 1945, and in all probability prior to 1 November 1945. Japan would have surrendered even if the atomic bombs had not been dropped, even if Russia had not entered the war. and even if no invasion had been planned or contemplated. - The United States Strategic Bombing survey (European war) (Pacific War) https://ia801903.us.archive.org/33/items/unitedstatesstra00cent/unitedstatesstra00cent.pdf