Wal-Mart (NYSE:WMT) was once the dominant company in retail, but those days are long over. Same-store sales are falling in the U.S., and international expansion has been a disaster. What's worse is that competitors are now outperforming the company, showing that other retail strategies are winning over Wal-Mart's low prices.

Before its own data breach issues, Target's same-store sales were up last year, outperforming its larger rival. A focus on design rather than just price is drawing higher-end customers who have cash to spend. 

But Amazon.com is the 800-pound gorilla taking share that's significant now that it has $78 billion in annual sales. Clearly, online retail is taking over, and Wal-Mart can't keep up. 

Motley Fool specialist Travis Hoium covers Wal-Mart's troubles and why investors should be cautious with the stock.