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.
Depression (economics)
The best-known depression was the Great Depression, which affected most national economies in the world throughout the 1930s. This depression is generally considered to have begun with the Wall Street Crash of 1929, and the crisis quickly spread to other national economies. Between 1929 and 1933, the gross national product of the United States decreased by 33% while the rate of unemployment increased to 25% (with industrial unemployment alone rising to approximately 35% – U.S. employment was still over 25% agricultural).