Let’s add 4: America was fighting on two theaters and the USSR was basically fighting on one (which isn’t to deny that their part of the war was by far the bloodiest). Subduing Japan and supporting the nationalists in China (the predecessors to the Taiwanese government) took enormous amounts of US military resources.
I’d downplay #2: WWII had all kinds of superweapon development programs, from the Manhattan Project to bioweapons to the Bat Bomb. The big secret, the secret that mattered, was which one would work. After V-J day the secret was out and any country with a hundred good engineers could build one, including South Africa. To the extent that nuclear nonproliferation works today, it works because isotope enrichment requires unusual equipment and leaves detectable traces that allow timely intervention.
Let’s add 4: America was fighting on two theaters and the USSR was basically fighting on one (which isn’t to deny that their part of the war was by far the bloodiest). Subduing Japan and supporting the nationalists in China (the predecessors to the Taiwanese government) took enormous amounts of US military resources.
I’d downplay #2: WWII had all kinds of superweapon development programs, from the Manhattan Project to bioweapons to the Bat Bomb. The big secret, the secret that mattered, was which one would work. After V-J day the secret was out and any country with a hundred good engineers could build one, including South Africa. To the extent that nuclear nonproliferation works today, it works because isotope enrichment requires unusual equipment and leaves detectable traces that allow timely intervention.