[ansy]

I'm not an economist, but as a student of history it seems America's dominance stems from being an arms dealer to Europe during both world wars, not getting its infrastructure razed to the ground in the process, and being both the bank and the builder for the resulting recovery.

It also doesn't hurt that the allies gave the US its best technological secrets during the war and the best minds from both sides emigrated to the US during and after the war.