Supply-side economics asserts that inflation is caused by either an increase in the supply of money or a decrease in the demand for balances of money. Thus the inflation experienced during the Black Plague in medieval Europe is seen as being caused by a decrease in the demand for money, the money stock used was gold coin and it was relatively fixed, while inflation in the 1970s is regarded as initially caused by an increased supply of money that occurred following the U.S. exit from the Bretton Woodsgold standard. Supply-side economics asserts that the money supply can grow without causing inflation as long as the demand for balances of money also grows.