Imagine the world is an apartment and its inhabitants are the countries of the world.
United States would be the occupant everyone needs. Sure, he might be a little showy but he pays eight-five percent of the rent, deals with the landlord and is always good for getting the beer and pizza. The rest of the occupants might not like him but they need him. Badly.
Now imagine some moron stuck our favourite occupant with an enormous bill no reasonable occupant really wanted anyway. Let's say this bill would cost- oh- about two trillion dollars (insert Dr. Evil image here). Utterly impossible to pay unless our go-to guy the United States involves his younger siblings and cousins to help him pay it off. He can't cover the rent or get the food and beer but this bill must be paid for or the moron will throw a tantrum.
Now the rest of the occupants are really stuck. The good-looking but part-time employed occupant, Canada, can't do it alone but the sniveling EU occupants and the in-need Third World occupants won't or can't. Forget about asking the Iranian or North Korean occupants hiding in their isolated rooms adorned with pictures of horror movie scenes and listening to Marilyn Manson at full-crank. And it's only a matter of time before they go off.
Now no one has rent, food or beer.
I never thought it was possible to hamstring the freest country on the planet but there you go!