The political and economic destruction in Europe caused by the First World War set the stage for the economic ruin of the Great Depression. This was a world-wide phenomena, exacerbated by poor tariff policies of the United States.
The US had become the major lender to Europe during the War, and the repayment by the former combatants was slow, as the industrial base of Europe was wiped out. Even so, France continued to hold Germany to its agreed upon reparations, which caused hyperinflation and once again destroyed the German economy in the 1920's.
The United States, being the only intact industrial power, expanded greatly during the 1920's particularly with the introduction of mass-produced automobiles and other consumer goods, many of which were exported.
But as Europe's governments failed to pay their debts, and Europe's people failed to purchase US consumer goods, the global market began to contract.
What finally brought down the US economy was widespread stock market manipulation, causing erratic high and low swings, until it crashed in October 1929. One of the more prominent businessmen who had clearly manipulated millions of dollars worth of stocks was Joseph P. Kennedy (1888 - 1969), father of the US president, who later as the first chairman of the SEC, forbade the "insider trading" and stock pooling that had made him a fortune, but triggered the Depression.