Down Stocks
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2015 wasn't a very remarkable year for the Dow Jones Industrials (DJINDICES:^DJI), which closed the year down more than 2% and weren't able to show a gain even after including dividends in the calculation. Part of the problem was that many stocks held the Dow back, with nearly half of the Dow 30 losing ground and with the worst five performers all losing 14% or more. Below, you'll learn more about the Dow's five biggest losers in 2015.

United Technologies (NYSE:UTX), down 14%
United Technologies came into 2015 in apparently great shape, riding the strength in the aerospace industry to new heights. But a decision to sell its Sikorsky helicopter division didn't turn out the way that many had hoped, as the deal appeared to benefit the buyer more than it helped United Technologies. The conglomerate is working to restructure itself with a new CEO at the helm, but weak conditions in many of its global market have cost it sales in its Otis elevator segment. Moreover, with weaker-than-expected commercial aftermarket sales of aerospace products, United Technologies disappointed investors looking for quicker results. Looking ahead, investors hope that the company will be able to accelerate its turnaround in 2016.

Chevron (NYSE:CVX), down 16%
Chevron's woes in 2015 were obvious to anyone who followed the financial markets, as the plunge in oil prices hurt the integrated oil company. Chevron responded by choosing not to make its traditional annual dividend increase, raising concerns that the oil giant could lose its status as a Dividend Aristocrat if crude doesn't recover. Moreover, delays in its key liquefied natural gas project in Australia have also threatened a key source of potential future growth. Until energy turns around, it'll be hard for Chevron shares to recover.

Caterpillar (NYSE:CAT), down 23%
Another casualty of energy was Caterpillar, whose heavy equipment sales once again posted big declines. Ongoing weakness in construction and infrastructure activity started Caterpillar's difficulties, and falling commodity prices in metals exacerbated the declines. With energy's drop, just about all of Caterpillar's key customer segments are down and out, and that has put a lot of pressure on the heavy-equipment manufacturer. The only good news is that once pent-up demand starts getting filled again, Caterpillar has plenty of room to bounce back. The question is when that will happen, and it could take longer than investors want.

American Express (NYSE:AXP), down 24%
American Express took a big hit early in the year, when major corporate-branded partner Costco said it would shift its credit card relationship away from the card giant. The move raised questions about American Express' staying power in the industry, because increasing competition has given the most valuable merchants more bargaining power in making deals with card-network providers and issuing financial institutions. To recover, American Express will need affluent shoppers to start spending again, and that could take a turnaround in global markets and a weakening U.S. dollar to execute completely.

Wal-Mart (NYSE:WMT), down 27%
The worst performer in the Dow was Wal-Mart, which faced a host of issues in 2015. Soaring labor costs resulted from the retailer's status as the favorite target for labor activists seeking higher wages, with Wal-Mart finally agreeing to pay a minimum wage of $9 per hour, which will rise to $10 in February. In addition, Wal-Mart expects to boost its spending on e-commerce development dramatically to fend off competition from its key online rival. Yet with these higher expenses, Wal-Mart still isn't seeing the growth that investors want. It could take years for the retailer to execute its long-range strategy, and there's no guarantee that the brick-and-mortar giant will succeed in its attempts.

Investors didn't do well by investing in the Dow, and these stocks were largely to blame. These five companies can teach you the valuable lesson that even blue-chip stocks can post big losses and that you have to work hard to avoid what can become substantial declines for your portfolio.

Dan Caplinger has no position in any stocks mentioned. The Motley Fool recommends American Express and Chevron. 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.