One glance at the market's performance makes it look like something terrible happened over the weekend. Yet unless you're a Greek soccer fan, it's hard to point to anything terribly new that's giving investors heartburn. Sure, Europe is still up in the air, with the European Union having its summit later this week. And health-care investors are waiting impatiently for the Supreme Court's ruling on health-care reform. But none of that is particularly new -- yet the Dow Jones Industrials (INDEX: ^DJI) fell sharply at the open and were down more than 160 points just after 10:45 a.m. EDT.

As usual, the banking and construction areas of the Dow were hit hardest, with Bank of America (NYSE: BAC), Caterpillar (NYSE: CAT), and JPMorgan Chase (NYSE: JPM) leading the losers, all down around 3%. One of the big focuses of the economic summit in Europe is addressing the problems with Spain's banking system, and if European leaders can't figure out a credible way to nip those problems in the bud before they spread even further, the growing crisis would eventually pose a threat to both B of A and JPMorgan.

Meanwhile, Caterpillar's decline seems to be due simply to the troubles throughout the global economy. The construction equipment giant may not be entirely reliant on Europe, but it still counts on European demand to drive production in the U.S. as well as China and other faster-growing areas of the world. Just as General Electric (NYSE: GE) has had to restructure its operations in Europe in order to take better advantage of more promising business prospects elsewhere, Caterpillar needs to keep its focus where it can maximize its profits in order to reverse its precipitous share-price decline over the past few months.

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