If Japan hadn’t attacked Pearl Harbor or the Philippines, and had never throughout the course of its war in the Pacific and in China, attacked any U.S. ship, base, civilian or military property, and had not killed any U.S. soldiers or civilians, but did invade and conquer the Indonesian archipelago, New Guinea, Southeast Asia, and selectively “skipped over” the Philippines and Hawaii, and neither did any of the Axis powers do anything of the above that Japan did not do, could Roosevelt ever had successfully asked Congress for a declaration of war?
If the U.S. had not entered the Second World War, and it had been fought to a victorious conclusion by the British Empire and the Soviet Union, although not necessarily an unconditional surrender, but a decisive military victory more conclusive than the victory won by the Triple Entente in the First World War but less so than unconditional surrender, would:
-America have developed an atom bomb, or have completed/started the Manhattan Project?
-Assuming the Soviet Union emerged the victor on the Eastern Front and on the Manchurian front, much as it did in actuality, but with significantly more casualties on the former and a greater length of the war by not more than a year, would the Soviet Union be the sole superpower in the world? If so, how much more powerful would the Soviet Union be than the British Empire and the United States?
-Comparing the U.S. and the U.S.S.R. directly in such a situation, could America, having stayed out of the war as I assumed it occurred, have become a superpower purely on its potential military strength as estimated by its economy, or would the gap between the U.S.S.R. and the USA, as a consequence of the latter’s non-participation, have become large enough militarily so that the U.S.A couldn’t be considered an equal in military sense?
Would this military gap, if it would have existed by 1946-7, would have been a permanent one in which the U.S. lack of participation in the War would have made it nearly impossible for the U.S. military to gain parity with the Soviets, or would the economy eventually render the U.S. an equal or greater power, regardless of whether the military fought. In other words, could America have become a superpower without fighting?
Ignoring all of the alternate history above, with the only distinction being that the Manhattan project failed and the scientists in the project were stumped before the end of the war, before either the US or the USSR obtained nuclear weapons, was there a significant difference between the military strength in a purely conventional sense between the two nations? More to the point, would you be worried about losing a total conventional war against the Soviet Union in 1945 (assuming you’re American I guess), as Germany did against them, if neither of the two nations would throughout the course of the war obtain the atom bomb or H bomb, or would you feel assured of victory in the end, and only be aghast at the cost of lives necessary to achieve that end? If it came down to an unconditional surrender, would you feel confident that you, and not Stalin, would be the victor?
Personally, I believe that the reason why the United States became a military superpower was because Japan attacked the U.S. in late 1941, but that it would remain the largest economy, with this margin over any other nation growing larger after the war until it became overwhelming, at least until 1960-5.