The Federal Reserve recently lowered interest rates for the first time this year. Companies went on to generally report strong earnings, and investors maintained optimism that potential interest rate cuts might further support growth. But, amid this bright picture, Federal Reserve chair Jerome Powell just delivered a dire warning to Wall Street. History offers us a strikingly clear picture of what may be next for the stock market and investors. So, if history is a guide, with stocks at historically pricey levels, the S&P 500 could be heading for a decline.