U.S. stocks declined on Thursday, pushing the Dow further into the red for the year, as Wall Street echoed action in European markets amid unease over the crisis in Ukraine.
"Putin is still the big wild card in all of this," said Chris Gaffney, senior market strategist at EverBank Wealth Management, referring to Russian President Vladimir Putin.
European shares fell amid media reports that had NATO Secretary General Anders Fogh Rasmussen urging Russia to "step back from the brink" by withdrawing troops and stopping its support of rebels in Eastern Ukraine.
"It's the yo-yo action in Europe that we keep following, as they sold off, we sold off," said Peter Boockvar, chief market strategist at the Lindsey Group.
Read MoreNATO chief in Kiev
"If tensions escalate, what does that do to the markets: It drives people to dollars, and into Treasuries for liquidity safe haven, and keeps a lid on interest rates here in the U.S.," said Gaffney.
"Escalations in Russia-Ukraine tensions definitely have a bigger impact on Europe than here. U.S. companies are somewhat protected," Gaffney added.
Another conflict had President Barack Obama reportedly weighing airstrikes against the Islamic State in Iraq and Syria, or ISIS, or airdrops of food and medicine to aid as many as 40,000 religious minorities in Iraq.
"Many people are itching, waiting for a correction, since we've gone so long without one. But we would say it's not justified by earnings expectations, as they continue to show improvement," said Nick Raich, CEO at the Earnings Scout.
Wendy's reported quarterly profit just shy of estimates and revenue that exceeded forecasts, with shares of the fast-food chain rising; Keurig Green Mountain reported quarterly profit the beat estimates and hiked its full-year outlook, with shares of the one-cup coffee brewers gaining.