Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

Even in the middle of earnings season, global economic issues have started to play a key role in the stock market's moves in 2014. After spending much of 2013 focused almost solely on improving conditions in the U.S. economy, today's 166-point drop in the Dow Jones Industrials (DJINDICES:^DJI) as of 11 a.m. EST reflects some of the stresses in key foreign economies such as China. Even with favorable earnings reports that sent Microsoft (NASDAQ:MSFT) and Procter & Gamble (NYSE:PG) higher this morning, worries about emerging-market inflation and capital outflows show that even the U.S. market is vulnerable to financial crises overseas.

On the earnings front, Procter & Gamble led the Dow's gainers, rising 3.5% even as its quarterly earnings fell 16% from year-ago levels. The consumer-products giant was able to beat expectations, and investors are increasingly satisfied that the company has turned some previous challenges around and could continue to boost its growth prospects. Yet trouble in emerging markets could weigh on P&G's long-term results, especially given the importance of rising standards of living to increase the number of middle-class customers in those markets and boost sales of P&G products.

Similarly, Microsoft rose almost 2% after beating earnings estimates by a substantial margin. Strength in consumer hardware helped the tech juggernaut post earnings per share that were a dime higher than investors had expected. Still, Microsoft also could face headwinds if key emerging regions suffer economic slowdowns, as its handset strategy will likely involve trying to capture more market share internationally given its relatively weak position in the U.S.

More broadly, though, the Dow's poor performance today reflects the fact that almost all of the blue-chip index's 30 stocks have substantial international exposure, especially to emerging-market countries. Fast-food giant McDonald's (NYSE:MCD) has made China a key part of its overall growth strategy, and any headwinds in emerging markets could be a major stumbling block for future growth opportunities. Even if the U.S. economy recovers more strongly, the lesson from the increasingly global economy is that the Dow will feel the pain from international markets, and smart investors need to take that into account in making long-range investing decisions.