I think it's down to the military, to be honest (Note: I'm completely biased by my own affiliation with the Navy).

However Coca-Cola may have got their start, they are now a multinational and can't be claimed to have any great allegiance to U.S. interests.

The military is what gives the U.S. the clout to work diplomacy and lead policy amongst the nations. I think the best example of this is the South China Sea which is looking increasingly resource-rich. China has expressed great interest in this region (right up to the borders of the Philippines, Vietnam, Malaysia, etc.), and is currently on a crash program to greatly expand the PLAN (People's Liberation Army Navy).

This is one of the driving reasons that President Obama and the DoD have enacted a "strategic shift" to the Pacific/Asia area because even in areas where the U.S. doesn't have a direct economic interest, the U.S. has indirect economic interests, in keeping natural resources within the effective economic control of their allies.

China has already heavily clamped down on rare earth production as a tool of economic and international political policy, so they've already demonstrated that they are willing to use monopolies on natural resources to their advantage (I'm not saying this to complain; just calling it how it is).

Money has substantial underpinnings in psychology (which is to say its value fluctuates wildly depending on what people think it's worth). And, sometimes you can't simply buy a country off. China is the example now, but for much of the period you discuss the example was the U.S.S.R. The Marshall Plan was successful in helping Europe recover, but the U.S.S.R. didn't allow its satellite nations to participate, and this isn't even going into the U.S. and Allied military efforts that kept the U.S.S.R. from expanding even farther.

When diplomacy fails the last resort for a nation's interests is the military, and the perception that its services are actually available.

I agree with rayiner on this much; Americans on average are very well off compared to much of the rest of the world. I would go further to say that Americans don't understand that their great advantage was never automatic. Not in the past; not in the future.

Now, given that the U.S. military was off doing what it was doing it would be foolish to claim that the follow-on economic effects weren't also important in U.S. hegemony, but I don't think economic factors played the major role.