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 in the United States
The Wall Street Crash of 1929 is often cited as the beginning of the Great Depression. It began on October 24, 1929, and was the most devastating stock market crash in the history of the United States. Much of the stock market crash can be attributed to exuberance and false expectations. In the years leading up to 1929, the rising stock market prices had created vast sums of wealth for those invested, in turn encouraging borrowing to further buy more stock. However, on October 24 (Black Thursday), share prices began to fall and panic selling caused prices to fall sharply. On October 29 (Black Tuesday), share prices fell by $14 billion in a single day, more than $30 billion in the week. The value that evaporated that week was 10x more than the entire federal budget and more than all of what the U.S. spent on World War I. By 1930 the value of shares had fallen by 90%.