Source: Microsoft.

After a brief hiatus to consider global economic and geopolitical news, investors turned their attention back to the earnings front Tuesday, and they didn't like what they saw. Poor results from Microsoft (NASDAQ:MSFT) sent ripples across the technology industry, and warnings from Pfizer (NYSE:PFE), Procter & Gamble (NYSE:PG), and Caterpillar (NYSE:CAT) all weighed on their respective sectors as the markets went into a minor tailspin. As of 12:35 p.m. EST, the Dow Jones Industrials (DJINDICES:^DJI) were down 311 points, and broader market benchmarks had declined 1% to 2% as well.

What pulled down the market today?

Source: Caterpillar.

There are definitely some common obstacles that all four of the Dow stocks mentioned above face. With a strong U.S. dollar, any company that does business around the world will see the value of its international sales decline, and currency impacts have brought down earnings for a while now. In particular, Caterpillar is already seeing a weaker environment due to low commodity prices, and with oil having joined the downward trend during late 2014, the heavy-equipment maker could continue to see further headwinds.

Yet Microsoft showed the biggest losses in the Dow, plunging 8.5% as investors assessed its latest results. Throughout much of last year, Microsoft saw unexpectedly strong results for its Windows division as the company's decision to stop supporting the Windows XP operating system forced many longtime customers to buy new hardware running more up-to-date operating systems. Yet during the most recent quarter, Windows licensing revenue to original-equipment manufacturers dropped 13%. The news was bad enough to pull down PC-chip giant Intel's (NASDAQ:INTC) shares more than 4% in sympathy, as Intel will also suffer if PC sales return to their long-term downward path.

Source: Microsoft.

The weakness of the PC comes as no true surprise to Microsoft. CEO Satya Nadella emphasized that Microsoft's transformative efforts rely on "executing against our strategic priorities and extending our cloud leadership," once more making it clear that mobile and cloud-based platforms are more important to the company's long-term success than software and services on traditional desktop machines. Nevertheless, Microsoft still relies on Windows and office-productivity software to drive a huge portion of its overall sales and profits, and despite efforts to make its upcoming Windows 10 software even more universal for mobile and desktop applications alike, the trend toward the death of the PC will weigh on Microsoft's results for years to come.

With the U.S. stock market having held its ground admirably for years without a major correction, investors are looking for any catalyst that could bring on a bigger downturn than the short-lived 3%-5% dips we've seen on a regular basis. If poor earnings results persist as the dollar strengthens yet further, then currency effects could well become the cause of a long-awaited pause in the bull market.