http://www.nytimes.com/2015/08/22/business/dealbook/global-markets-fall-for-second-day.html?hp&action=click&pgtype=Homepage&module=first-column-region&region=top-news&WT.nav=top-news&_r=0

Stock prices around the world continued to plunge on Friday, threatening to end one of the longest bull runs in the history of the United States stock market.

A searing six-year rally in United States stocks had advanced into the summer months, shrugging off challenges like the dispute over Greece’s debt that nearly led to the country crashing out of the euro. But in the last two weeks, world markets tumbled as investors grew increasingly concerned about economic conditions in China, which unexpectedly devalued its currency last week, and the outlook for the economies of other large developing countries.

As the selling accelerated Friday afternoon, some benchmark indexes were at or near 10 percent below their recent peaks — a “correction” in Wall Street parlance. “This is likely going to go down as the first meaningful correction in four years,” said David Rosenberg, an economist and strategist at Gluskin Sheff.

Sell-offs in the financial markets need not cause harm in the real economy. In many cases in the postwar period, the United States stock market has recovered after reacting negatively to problems overseas. Strong employment numbers and other economic indicators suggest that the United States economy remains resilient.

Still, fear in financial markets can feed on itself. And the declines in the markets are coming not only as China struggles, but also as the Federal Reserve is winding down its huge stimulus efforts. Trillions of dollars of cheap money from the Fed has fueled economic growth and helped push markets higher around the world. Now, the question is whether the world can stay on the recovery path without the Fed’s largess.

Such concerns on Friday helped push stocks far below the peaks they reached just weeks ago when investors were ebullient. The Dow Jones industrial average is more than 10 percent below the high it reached in May. At Friday’s close, the index was down 530.94 points, to 16,459.75, a loss of 3.1 percent on the day.

The Standard & Poor’s 500-stock index, a broader benchmark, fell below the psychologically important 2,000 mark. It was down 3.2 percent on the day and more than 7 percent below its recent peak. It fell 64.84 points, to 1,970.89. The index lost $1.14 trillion in value this week, according to S.&P.