In 1970, General Motors was the largest and most profitable company in America. Today, of course, GM is neither. Instead, in 2009 America’s largest company is Wal-Mart, which was still only a regional, privately-held retailer in 1970. Wal-Mart’s rapid rise is not unique, however. Among the 100 largest firms today, a number—including FedEx, Microsoft, Cisco, and Home Depot--didn’t even exist in 1970. So profoundly has the landscape changed that 80 percent of the Fortune 100 companies today are different from 1970.