Ukraine President Petro Poroshenko said Russian forces had entered his country. He called an emergency meeting of the nation's security council. The yield on the 10-year Treasury note declined as investors sought out lower-risk assets.
A string of disappointing earnings and profit outlooks late Wednesday and early Thursday also weighed on the market early on.
Not all the news was discouraging.
The Commerce Department estimated that the U.S. economy grew at an annual rate of 4.2 percent in the April-June quarter.
The Labor Department added to the good news, saying the number of Americans seeking unemployment benefits slipped last week to 298,000, a low level that signals employers are cutting fewer jobs and hiring is likely to remain strong.
"The economic data in the U.S. continues to look quite good," Davidson said.
Nonetheless, major U.S. stock indexes opened lower. They pared some of their losses as the day went on, but remained down the rest of the day.
All told, the Standard & Poor's 500 index fell 3.38 points, or 0.2 percent, to 1,996.74. The index hit record highs the first three days of the week.
The Dow Jones industrial average slid 42.44 points, or 0.3 percent, to 17,079.57.
The Nasdaq composite shed 11.93 points, or 0.3 percent, to 4,557.69.
Major U.S. indexes are on track to end higher for the month and are up for the year.
Trading volume was lighter than the recent average ahead of the Labor Day holiday.
Investors seized on the lackluster earnings to reduce their holdings in several retailers.
Williams-Sonoma tumbled 12 percent after the cookware and home furnishings company issue a disappointing full-year profit outlook late Wednesday. The stock shed $8.96 to $65.93.