In November 2000 Iran...

In November 2000, Iraq stopped accepting U.S. dollars for their oil.  Counted as a purely political move, Saddam Hussein switched the currency required to purchase Iraqi oil to the euro. 
Selling oil through the U.N. Oil for Food Program, Iraq converted all of its U.S. dollars in its U.N. account to the euro.  Shortly thereafter, Iraq converted $10 billion in their U.N. reserve fund to the euro.  By the end of 2000, Iraq had abandoned the U.S. dollar completely. Two months after the United States invaded Iraq, the Oil for Food Program was ended, the country's accounts were switch back to dollars, and oil began to be sold once again for U.S. dollars.  No longer could the world buy oil from Iraq with the euro.  Universal global dollar supremacy was restored.  It is interesting to note that the latest recession that the United States endured began and ended within the same timeframe as when Iraq was trading oil for euros.  Whether this is a coincidence or related, the American people may never know.