With the patron’s gold reserves was composed of only gold (in those countries that had adopted such a system). But under the Bretton Woods system, the United States fixed the exchange rate of the dollar with gold, and allowed convertibility of dollars into gold, turn the other central banks use the dollar instead of gold as a reserve. This helped create the impression that in fact the dollars are so reliable and secure as gold. However, due to the U.S. government budget deficit (especially due to the war in Vietnam), the dollar just by ceasing to be a convertible due to a large increase in the emission of currency without a proportional increase in gold reserves by the United States, which term credibility. But after this, the dollar remained stable until the paper money world financial and mortgage crisis that began in 2007 and unleashed panic came in March 2008 so this no longer the most important reserve currency, and this increase the use of the euro as a reserve currency after its introduction and gold.