Fake money.

The Impact of Fiat Money as the World’s Reserve Currency

The creation of fiat official government money has had a profound effect in history and on our nation and the world today. "Fiat" means it is worth whatever the government says it is (its face value), although the material of which it is made may have more or less intrinsic market value. Examples would include both valuable silver dollars and worthless paper, each declared to be worth $1; and today’s American Eagle bullion coin with a face value of $50 for one ounce of gold.

Normally, when a country creates too much fake money, sellers avoid it for payment, or stop buying its bonds due to its falling value, and the party is soon over. However, the U.S. is in a unique position never seen in the history of the world. Our fiat paper money is the primary de facto world’s "reserve currency" (anyone will accept it for payment and keep it as cash, or as a dollar-denominated asset; banks keep it as their reserves, like gold). We can create new money out of thin-air, and sellers of goods and services worldwide will accept it. We can also pay our debts with it, even as the federal government spends to excess.

Link:
http://www.activistpost.com/2010/09/impact-of-fiat-money-as-worlds-reserve.html