The U.S. stock market has been stumbling since the beginning of the year. Now, Russia’s escalating conflict with Ukraine is adding considerably to the market’s problems.After President Vladimir V. Putin of Russia ordered troops to enter two separatist-controlled enclaves in Ukraine, the S&P 500, which often serves as a proxy for the U.S. stock market, also crossed a notable threshold.By the market close on Tuesday, the S&P 500 fell to 4,304.76, down 1.01 percent for the day. That wasn’t much of a loss. Yet that incremental decline nonetheless represented a notable milestone. It brought the stock market down 10.3 percent from its most recent peak on Jan. 3.In Wall Street jargon, that meant the S&P 500 had a “correction,” because its losses since Jan. 3 exceeded 10 percent.That 10 percent definition is entirely arbitrary and the subject of many quibbles, but this much is clear: A correction is not a good thing.“It’s an early warning indicator that tells you the market isn’t heading in the direction you want it to be going in,” said Edward Yard …
