Also known as "the man who financed the Civil War," because he started a 1873 financial collapse, aka The Panic of 1873. This, in turn sparked a severe nationwide depression. On January 1, 1861, Cooke established Jay Cooke & Company in Philadelphia.
 He invested in the Northern Pacific Railroad, but the railroad's continuing loss of money and a general bad money market caused insolvency and Jay Cooke & Company folded. The fall of Jay Cooke and Co.  started a financial panic wherein several companies went bankrupt and the stock market crashed. Overspeculation and a lack of money caused a nationwide depression that affected millions of people for the rest of the decade.

Panic of 1873 (ABC Clio)(Secondary)

The panic of 1873 was New York City Stock Exchange's collapsing of the large investment from Jay Cooke and co. because of their investing too heavily in railroad securities. The collapse affected the entire stock market, and soon other large eastern firms failed. By 1875, about 500,000 men were unemployed, and a pay decrease for other workers caused a wave of strikes and labor violence. Thousands of stock market investors were ruined by the panic and resulting economic depression. It took until the 1880s for the American enomony to start to improve.