We were trying to get the USSR to attack Japan for 3 years. It was only after we had complete dominance that we quit pressuring Stalin to declare. He feared that Japan would move into Siberia. Stalin never trusted the USA or Britain, though Roosevelt was foolishly maive in his assessment of Stalin. Remember that the USSR finally did declare war, right before the end, in order to size some islands. The Kurils, if memory serves me. We paid dearly in blood for the USSR to demand a place on the USS Missouri.

Concerning not looking into the future for the nuclear bomb -- quite right. Just as one shouldn't look into the future to determine taht the USA could not sustain a lengthy war. We fought a war of pure aggression (on our side) with the Indians for 100 years. Later we fought in Vietnam for 10. We will soon pass the 10 year mark in Afghanistan and Iraq. There is no magic number. There is the political will and the ability to sustain the people. That's a political, not military problem.