There really is no way to prevent the stock market from crashing. However, governments have added safeguards to prevent severe drops and upsets in market stability.  One such tactic is the circuit breaker, instituted after the 1987 crash. If the S&P 500 Index experiences a drop of 7% or more over the previous day, trading in all US stock markets is halted. Depending on the severity of the drop, trading could be suspended for either a 15-minute period or the rest of the day. The purpose of this measure is to give analysts and investors time to gather enough accurate information before making trade decisions.  Large amounts of stocks might also be purchased by private investors to try and stabilize a market. In fact, that used to be quite effective a century ago, shortening the Panics of 1873 and 1907. The government itself can step in, lowering interest rates to encourage investors to borrow and buy. But even with these mitigating factors, crashes still happen.