We are a Wal-Mart Nation. Wal-Mart's influence on the U.S. economy has reached levels not seen by a single company since the 19th-century rise of Standard Oil, economists and historians say. Although Wal-Mart is hitting speed bumps because of growing labor challenges, employment lawsuits and higher costs, few doubt it will stop besting competitors as it expands. While other retailers such as Home Depot, tech giants such as Microsoft and manufacturers such as General Electric played big parts in the 1990s productivity gains, Wal-Mart, with its massive buying power and technology advantage, played the biggest role, economists say. As it grows, its influence, largely unknown to consumers, will continue to seep into more parts of the USA and the global economies.