<P> No definitive conclusions have been reached on the reasons behind the 1987 Crash . Stocks had been in a multi-year bull run and market P / E ratios in the U.S. were above the post-war average . The S&P 500 was trading at 23 times earnings, a postwar high and well above the average of 14.5 times earnings . Herd behavior and psychological feedback loops play a critical part in all stock market crashes but analysts have also tried to look for external triggering events . Aside from the general worries of stock market overvaluation, blame for the collapse has been apportioned to such factors as program trading, portfolio insurance and derivatives, and prior news of worsening economic indicators (i.e. a large U.S. merchandise trade deficit and a falling U.S. dollar, which seemed to imply future interest rate hikes). </P> <P> One of the consequences of the 1987 Crash was the introduction of the circuit breaker or trading curb on the NYSE . Based upon the idea that a cooling off period would help dissipate investor panic, these mandatory market shutdowns are triggered whenever a large pre-defined market decline occurs during the trading day . </P> <P> On September 16, 2008, failures of massive financial institutions in the United States, due primarily to exposure to packaged subprime loans and credit default swaps issued to insure these loans and their issuers, rapidly devolved into a global crisis . This resulted in a number of bank failures in Europe and sharp reductions in the value of stocks and commodities worldwide . The failure of banks in Iceland resulted in a devaluation of the Icelandic króna and threatened the government with bankruptcy . Iceland obtained an emergency loan from the International Monetary Fund in November . In the United States, 15 banks failed in 2008, while several others were rescued through government intervention or acquisitions by other banks . On October 11, 2008, the head of the International Monetary Fund (IMF) warned that the world financial system was teetering on the "brink of systemic meltdown". </P> <P> The economic crisis caused countries to close their markets temporarily . </P>

When did the stock market crash in 2008