Reserve currency before the beginning of the worldwide credit crunch related recession and Eurozone crisis, which harmed the euro and slowed its adoption. Since 2009, the reserve currency use of the euro has continued to drop, down to 23.9 percent in 2013. The Dutch guilder was the "de facto" reserve currency in Europe in 17th and 18th centuries. The United Kingdom's pound sterling was the primary reserve currency of much of the world in the 19th century and first half of the 20th century. The emergence of the USA as an economic superpower, and the establishment of the U.S. Federal Reserve System
Currency substitution financial assets denominated in a foreign currency. It can also occur as a gradual conversion to full currency substitution, for example, Argentina and Peru were both in the process of converting to the U.S. dollar during the 1990s. "Dollarization", when referring to currency substitution, does not necessarily involve use of the United States dollar. The currencies that have been used as substitutes have been the US dollar, the euro, and the Australian dollar. After the gold standard was abandoned at the outbreak of World War I and the Bretton Woods Conference following World War II, some countries sought exchange rate