(Close:) Wall Street fell for a third straight day after the US launched a major bombing raid on an ISIS complex in Afghanistan.
Investors were also digesting a wave of results from major US banks.
The Dow Jones index lost 138.61 points, or 0.67%, to 20,453.25 while the S&P 500 shed 15.98 points, or 0.68%, to 2,328.95.
The tech-heavy Nasdaq fell 31.01 points or 0.53% to 5,805.15.
The Afghan attack followed days of mounting concerns about US relations with Russia and North Korea.
JJ Kinahan, a market strategist at TD Ameritrade, told AFP: "People are saying, 'Let's take some risk off the table.' With what's going on in geopolitics, who knows what can happen."
Shares in JP Morgan Chase and Citigroup fell 1.17% and 0.8% respectively, despite both lenders reporting a 17% hike in quarterly profits.
And Wells Fargo shares fell 3.3% after the bank reported a drop in mortgage banking revenue.
Oil-linked shares also slipped as investors appeared to cash in gains made earlier in the week.
ExxonMobil and Chevron lost 1.5% and 2.6% respectively, while Halliburton slid 1.9%.