Faltering expectations drove the markets today, forcing the S&P 500 (INDEX: ^GSPC) to dive 0.81% despite a lack of substantial macroeconomic data. Instead, some troubling individual earnings reports foretold a bad earnings season in the minds of many investors.

World economics delivered conflicting reports. Investors originally cheered confirmation of the EU's bailout initiatives for Spain, but those reactions quickly gave way to fresher headlines elsewhere. A Pentagon report to Congress also revived a months-old storyline: The Iranian military continues to improve missile accuracy, reigniting fear in the minds of some for heightened global conflict.

At the end of the day, though, earnings expectations provided the fireworks. Advanced Micro Devices (NYSE: AMD) suffered a massive 11.21% cut, citing China's and Europe's weakness for its unexpected Q2 sales plunge. AMD originally forecasted a 3% spike, but revenue instead dropped 11% to $1.41 billion. The PC-processors manufacturer highlighted a terrible overall day for tech, with the Nasdaq Composite (INDEX: ^IXIC) losing 1%.

Industrial-goods manufacturer Cummins (NYSE: CMI) met a similar fate. After the company originally forecasted 10% revenue growth in 2012, emerging-market stagnation forced it to readjust projections back to 2011 numbers. The company did, however, increase its dividend up to $0.50 per share, or a 25% increase over the previous $0.40 dividend. Investors obviously viewed the move skeptically, and shares dropped 8.94%.

J.C. Penney (NYSE: JCP) rounded out the big losers on the day. The department-store giant dropped almost 6% after a few big developments. It laid off 350 corporate workers today, the second major cut in corporate jobs this year, as part of a major remodeling effort that targets a $900 million cost decrease by the end of this year. Investors may be punishing J.C. Penney over pessimism regarding its jobs news, but a recently revised analyst outlook is contributing to the slide as well. Credit Suisse analyst Michael Exstein expects a second-quarter sales decrease worse than the first quarter's 20% drop. Ultimately, the revenue losses may become irrelevant, since retailers generally use massive fourth-quarter sales to drive yearly revenue.

Enough companies suffered harsh earnings revisions to call it a pattern, however, and that could mean bad news for the overall markets. J.C. Penney could easily adjust if it meets its $900 million target in cuts, but the sudden slowdown in emerging-markets growth has many investors troubled. Of course, this could all blow over tomorrow if companies begin to beat earnings reports, but a global slowdown would mean smaller returns for a much longer time period.

The easiest next move for the smartest investors: Stay alert. Volatility will continue to plague the markets, making it vital for every investor to track the important companies. With earnings reports upon us, stay up to date on all the news and analysis using your free My Watchlist feature. company below to get started: