My basic point was that changing a single variable in the course of WWII – even something as huge as the development of nuclear weaponry – doesn’t necessarily or automatically translate into a fundamantal reversal of the war’s outcome. One has to look at the details of such hypotheses, and one has to consider that other variables might change too as a result…and that those changed variables could themselves affect the outcome of the war.
Let’s take as an example the hypothesis you’ve just mentioned: “If those 2 bombs were dropped on London and Moscow instead of Hiroshima and Nagasaki, The Axis would’ve won the war.” Well, would that necessarily have been the case? If we assume that Nazi Germany had managed to mass-produce (not just produce) a nuclear arsenal (which it could not have; even the US, despite its massive nuclear program, only managed to crank out enough fissile material for a few bombs before the war’s end), then yes that would probably have been fatal to Britain and the USSR. Adding the further assumption that Nazi Germany also had a trans-oceanic bomber or missile delivery system for its A-bomb arsenal of dozens and dozens of weapons, having both the required range and accuracy, then this could potentially have been compelled the US to sue for peace. But would just two first-generation fission bombs, one aimed at London and one at Moscow, have produced an Axis victory? That’s less obvious.
Losing London and Moscow would have hurt Britain and the USSR badly, of course, but the relevant question is whether it would have been fatal to those two countries, especially if the British and the Soviets would have been aware (in this hypothetical scenario) that Germany only had two bombs and had shot its bolt. Countries at war stop fighting when they lose either the material ability to fight or the psychological will to fight, or lose both simultaneously. In June 1940, France folded because it lost the will to fight, even though it still had some substantial ability to do so. In 1945, Germany and Japan folded because they lost the ability to fight, even though they still had some substantial will to do so. Geographically and politically, both Britain and the USSR were theoretically in a position to continue prosecuting the war despite the loss of their capitals: Britain because of its hard-to-invade position as an island and because of its oceanic connections to a vast network of colonies, Commonwealth territories and allies such as the US, and the USSR because of its huge size and because of the fact that the invading Germans had done such a good job of motivating the Russian population to fight them at all costs. (Japan, it should be noted, was already collapsing economically and militarily when Hiroshima and Nagasaki were A-bombed. It was already on the brink of a precipice in August 1945; the A-bombs didn’t drive Japan there, they just pushed it over the edge.)
Moreover, if we assume that the state of preliminary nuclear research in the 1930s had been far enough advanced to allow Germany to produce two A-bombs by, let’s say, 1943, this could also mean that the US might itself have been nuclear-armed (and to an even greater degree than Germany) in 1943. In such a scenario, the nuking of London and Moscow by Germany would probably have soon resulted in the US nuking Berlin and Hamburg and every other German city for which a bomb was available. That would hardly have resulted in an Axis victory.
If I had to think of a plausible “bigger” cause for the Axis loss in WWII, I’d have to go with something so broad that it would encompass the many, many, many consitutuent factors of the war, and thus which could not be translated into a staightforward “if only they had done X rather than Y…” statement. To me, the fundamental error that Germany and Japan made was to bite off more than they could chew, without having a coherent set of “victory conditions” (to put it in A&A terms) that took into account the possibility that their enemies might have both the skill and the determination to resist. Some related points are that Germany and Japan both thought too much in military terms revolving around short-term maneuver warfare, and not enough in economic terms revolving around long-term attrition warfare, and that they both had a faulty psychological portrait of their enemies. Japan’s game plan for the Pacific, for example, was basically, “Attack the US by suprise, grab a bunch of territories quickly, inflict a few painful early defeats to the decadent, soft, isolationist, unmilitaristic and undisciplined Americans who have no convictions for which they’re willing to die, then sit down with them and negotiate a peace treaty that will allow Japan to keep all of its gains.” To most Japanese leaders of the time, whose understanding of Americans was (to put it mildly) thin and inaccurate, it seemed perfectly plausible that the Americans would dutifully go along with this game plan. When the Americans (again to put it mildly) went off-script after Pearl Harbor, Japan’s leaders basically ended up in a situation where their Plan A had been shot to hell and where no effective Plan B could be devised to replace it.
