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.
Wall Street Crash of 1929
The 1929 crash brought the Roaring Twenties to a halt. As tentatively expressed by economic historian Charles P. Kindleberger, in 1929, there was no lender of last resort effectively present, which, if it had existed and been properly exercised, would have been key in shortening the business slowdown that normally follows financial crises. The crash instigated widespread and long-lasting consequences for the United States. Historians still debate whether or not the 1929 crash sparked the Great Depression or if it merely coincided with the bursting of a loose credit-inspired economic bubble. Only 16% of American households were invested in the stock market within the United States during the period leading up to this depression, suggesting that the crash carried somewhat less of a weight in causing it.
However, the psychological effects of the crash reverberated across the nation as businesses became aware of the difficulties in securing capital market investments for new projects and expansions. Business uncertainty naturally affects job security for employees, and as the American worker (the consumer) faced uncertainty with regards to income, naturally the propensity to consume declined. The decline in stock prices caused bankruptcies and severe macroeconomic difficulties, including contraction of credit, business closures, firing of workers, bank failures, decline of the money supply, and other economically depressing events.