(CNBC) — U.S. stocks fell on Monday as global disapproval of Russian President Vladimir Putin increased after the downing of a passenger plane in Ukraine and amid international calls for a truce in the Israeli-Palestinian conflict.
"The world is a more dangerous place, and if you need an excuse to respond to the current levels of valuations, there's a really good excuse. Given the performance of the markets in 2013 and this year to date, common sense alone says maybe it's time to sell, or play it more safely," said Hugh Johnson, chairman of Hugh Johnson Advisors.
The fact that large capitalized companies have been outperforming small capitalized firms is telling, Johnson said. "In a bull market, that's a clear sign investors are becoming worried, and playing it safe. You can stay bullish, but you have to build a little defense."
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