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
World currency unit have adopted the name "World Currency Unit". The Wocu (contraction of World Currency Unit) is a standardized basket of currencies — the national currencies of the 20 largest national economies measured by GDP, established in 2008. The basket is reweighed semi-annually according to the relative growth of the economies, whereby constituent currencies are replaced by other currencies should the size of the GDP be overtaken by that of another national economy. Conceived as an apolitical and global alternative to the ECU, it is used as a reference currency for global investors and companies seeking to mitigate bilateral exchange rate volatility.