Deflation
Deflation occurred periodically in the U.S. during the 19th century (the most important exception was during the Civil War). This deflation was at times caused by technological progress that created significant economic growth, but at other times it was triggered by financial crises — notably the Panic of 1837 which caused deflation through 1844, and the Panic of 1873 which triggered the Long Depression that lasted until 1879. These deflationary periods preceded the establishment of the U.S. Federal Reserve System and its active management of monetary matters. Episodes of deflation have been rare and brief since the Federal Reserve was created (a notable exception being the Great Depression) while U.S. economic progress has been unprecedented.
Great Depression
Between 1933 and 1939, federal expenditure tripled, and Roosevelt's critics charged that he was turning America into a socialist state. The Great Depression was a main factor in the implementation of social democracy and planned economies in European countries after World War II (see Marshall Plan). Keynesianism generally remained the most influential economic school in the United States and in parts of Europe until the periods between the 1970s and the 1980s, when Milton Friedman and other neoliberal economists formulated and propagated the newly created theories of neoliberalism and incorporated them into the Chicago School of Economics as an alternative approach to the study of economics. Neoliberalism went on to challenge the dominance of the Keynesian school of Economics in the mainstream academia and policy-making in the United States, having reached its peak in popularity in the election of the presidency of Ronald Reagan in the United States, and Margaret Thatcher in the United Kingdom.