The 1873 financial crash that helped start the Long Depression was the Panic of 1873.
The panic began in Europe and the United States after the failure of the investment firm Jay Cooke & Company in September 1873. Jay Cooke had heavily promoted bonds for the Northern Pacific Railway, and doubts about railroad finance spread through markets. The New York Stock Exchange temporarily closed during the resulting turmoil.
The crisis ushered in a long period of weak prices, business failures, and unemployment, often called the Long Depression. Historians differ about its precise length and severity, so the name does not describe one universally measured period. The Panic of 1873 is also sometimes called the Great Depression of the nineteenth century, but that label can be confused with the 1930s Great Depression.