At present moment I can offer this simple explanation (hopefully I can provide a more detailed response later):

The end of WW2 firmly established the US as the Hegemon, the power among powers (the soviets may have been powerful but immediately following WW2 they could not match America in power). The position gave them more control in the world, and coupled with the fact that their potential rivals for economic control (most of Western Europe) was forced to spend years rebuilding themselves instead of improving their economic standpoint like the US did. Not to mention that the few decades after 1945 saw the final collapse of European imperialism and it was the global empires that first led to European powers.

I hope this helps for now!