The economy is in fact over-expanded, particularly in railroad construction, and the weak link turns out to be the banking house of Jay Cooke and Company, which helped the U.S. Government finance the Civil War and also underwrote the construction of the Northern Pacific Railroad. Jay Cooke and Company, a large and respected banking house declares itself bankrupt, and announces its failure on September 18, 1873.. (The bank's collapse precipitates the "Panic of 1873" and the ensuing three yea depression during which more than 10,000 businesses fail.     The basic economic problems are overproduction, a declining market and deflation. Investors in Europe, where a depression is already underway, begin to call in American loans. The New York Stock Exchange closes its doors for 10 days; other businesses fail; and railroad construction is curtailed, with some railroads defaulting on their bonds. The unemployed begin to move about the country seeking jobs, and bread lines appear in the cities. The hard times drove numbers of laboring people and those in humble circumstances to the West and other portions of the country, to seek the rewards which the stagnation of business in the great commercial centre denied them.