In his 1997 article "Post-WWII Western European Exceptionalism: The Economic Dimension", Delong goes on to describe in detail two alternative post-war histories for western Europe. In one, a western Europe that either was conquered outright by Stalin or was communized via mass elections; in the other, the lack of American economic aid would force western Europe to that retreat into the same kind of highly regulated national protectionism that eventually drove Argentina out of the First World. Paris, Madrid, Rome, and Frankfurt could have shared the same fates as Buenos Aires, save that they would have had much more menacing neighbours.
The United States could have decided, after its second expensive and initially unpopular involvement in an extra-hemispheric war, to retreat from western Europe and to allow the continent to rebuild itself as best it could. Isolationism was strong in the United States, after all, and the decision to commit the United States to a permanent alliance with the non-Communist countries of Europe--and at significant cost, too--was unpopular. Imagine a world with no Marshall Plan, therefore no European Economic Community and no trente glorieuses, no attractive models of consumer capitalism and social democracy to attract the subjects of Communist countries, no attractive targets for exports for nearby First World-aspiring countries, no embedding of West Germany firmly within a consensus-driven European framework, no continent-wide entrenchment of basic civil and political rights. As tempting as it is to draw an uninterrupted lineage from Coudenhove-Kalergi's Pan-Europa to the European Union of 2005, a case just can't be made that Europe was bound to be prosperous and democratic. The United States had to step in and act constructively. What would have been true for western Europe would, I suspect, also hold true for Japan, and still more for the rest of war-devastated Eurasia.
Canada and the Australasian dominions likely would have done well enough for the first generation after the United States' fateful decision, as would the United States itself. If anything, their status in the post-war world would be significantly greater thanks to the devastation of their potential rivals. In the longer run, it would have done decidedly bad things even to these favoured countries. What would the world be like, after all, if it was even poorer and less democratic than it is now? Quite probably it would be a rather more violent world: It's unlikely that a democratic Argentina with G-8 membership credentials as secure as Canada's would have invaded the Falkland Islands.
The United States might have neglected its role in the global balance of power after the First World War to the world's lasting regret. After the Second World War, though, it did a superlative job, not only averting the creation of a Soviet hegemony stretching from the English Channel to the Pacific, but that prevented western Europe from following Argentina's trajectory into economic decline and political chaos, and in so doing, saving the world from a rather nasty fate. It's quite demeaning (to the United States, to its intentions) to demand that the rest of the world pay obeisance to the United States because of this intervention. It also denies history to pretend that, for reasons not immediately in the United States' interest, the United States did something remarkably good.