In "Americans at War" Stephen Ambrose tells a story about Colonel Goodpaster, who helped draw up the invasion plans. He was in Japan doing a documentary 46 years after the war. The Japanese asked if it were true that the Russians would have been involved and he assured them that it was. One of the Japanese said "thank God you used the bomb."
Also, suppose you issue this ultimatum and go to put on your big demo in the harbor, and it doesn’t work? Just makes a splash...
What then?