By Stephan Bisaha Stock market numbers are displayed on the floor of the New York Stock Exchange during afternoon trading on March 03, 2026 in New York City. Stocks tumbled with the Dow Jones losing over 400 points amid a possible prolonged U.S.-Iran conflict. Michael M. Santiago/Getty Images hide caption Since the U.S. and Israel began strikes against Iran, oil prices have gone up. Stock markets have gone in the opposite direction, driven by uncertainty about the war's future and its effect on the economy. The Dow Jones Industrial Average is down around 9% since its February high, which it hit about two weeks before the war began. That's far from a crash or being considered a bear market, which typically describes a market that's fallen 20% from recent highs. But the market decline has pulled down the value of Americans' investments funds, from college to retirement plans. What should you do if that makes you feel as jittery as the markets?…