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.

The stock market saw early gains almost completely evaporate in just a matter of hours. Initially, optimism about solid economic data made investors optimistic, pushing the Dow Jones Industrials (DJINDICES:^DJI) to early gains of more than 100 points. But as it looks increasingly likely that the U.S. will strike against Syria, the threat of war dampened investor enthusiasm, and the Dow closed with a gain of just 24 points. The broader market held onto slightly more of its gains, with the S&P 500 ending higher by almost half a percent.

What was particularly surprising, however, were declines among some of the Dow's most influential stocks in light of interesting M&A activity. Microsoft (NASDAQ:MSFT) closed the day down more than 4.5% as shareholders rebelled against the company's decision to buy out partner Nokia's (NYSE:NOK) mobile division for $7.2 billion. Nokia's shares soared more than 30%, but investors in Microsoft clearly fear that the company dramatically overpaid simply to bolster its presence in the mobile-hardware market. The big question is whether getting access to Nokia's intellectual property and experienced personnel will help it break a string of hardware-related failures.

Verizon (NYSE:VZ) also slumped today, falling almost 3% after announcing its own plans over the weekend to buy out the 45% stake in the Verizon Wireless joint venture that it doesn't currently own from Vodafone (NASDAQ:VOD) for $130 billion. For Verizon, the deal answers long-held questions about where future growth will come from, as it essentially doubles down on the future health of the U.S. business. Interestingly, Vodafone shares also fell on the news, as its shareholders likely were disappointed by Verizon's failure to buy out the company outright. In fact, Vodafone's market cap tells the tale of just how important Verizon Wireless has been to the British telecom, as the value of the deal leaves only about $25 billion worth of value from the remainder of Vodafone's telecom businesses around the world. It'll be interesting to see what Vodafone does with its new cash hoard and whether potential acquirers become interested in Vodafone.

Finally, AT&T also lost ground with a drop of about 1.5%. Verizon's move raises questions about how the second-largest U.S. wireless carrier will respond. Some have argued that it might be a natural choice to buy the shell of Vodafone, especially given AT&T's recent interest in some other international telecoms. Yet reflexively making an acquisition of its own simply to match Verizon's M&A move won't make sense for AT&T unless it also furthers its long-term strategy. Until investors can figure out exactly what that strategy is, the uncertainty could hold AT&T shares back in the short run.

Fool contributor Dan Caplinger has no position in any stocks mentioned. You can follow him on Twitter @DanCaplinger. The Motley Fool recommends Vodafone and owns shares of Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.