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.
Wealth inequality in the United States
Pioneering work by Simon Kuznets using income tax records and his own well-researched estimates of national income showed a reduction of about 10% in the portion of national income going to the top 10%, a reduction from about 45–50% in 1913 to about 30–35% in 1948. This period spans both The Great Depression and World War II, events with significant economic consequences. This is called the Great Compression.