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 The WCU – World Currency Unit (WCU) is an indexed unit of account that stands for a unit of real global purchasing power. Since each unit by design represents a stable unit of purchasing power, the stipulated interest rate on WCU-denominated bonds represents a real interest rate. In principle, the common denomination of bonds by issuers from different parts of the world using the WCU, as well as the greater transparency of real interest rates, will produce more efficient capital markets, as savers and borrowers around the world converge in their understanding of what each basis point of interest means