In the early years, the league was not stable and teams moved frequently. Franchise mergers were popular during World War II in response to the scarcity of players. An example of this was the Steagles, temporarily formed as a merger between the Pittsburgh Steelers and Philadelphia Eagles.
Franchise moves became far more controversial in the late twentieth century when a vastly more popular NFL was free from financial instability and allowed many franchises to abandon long-held strongholds for perceived financially greener pastures. This was done in spite of the promises to Congress by Pete Rozelle in 1966 that if the AFL-NFL merger were allowed, no city would lose its franchise. Those promises were made to ensure passage of PL 89-800, which granted anti-trust immunity to the merged professional football leagues. While owners invariably cited financial difficulties as the primary factor in such moves, many fans bitterly disputed these contentions, especially in Cleveland (the Rams and the Browns), Baltimore (the Colts), Houston (the Oilers), and St. Louis (the Cardinals), each of which eventually received teams some years after their original franchises left (the Browns, another Browns, Ravens, Texans, and Rams, respectively). Notably, Los Angeles, the second-largest media market in the United States, has not had an NFL team since 1994 after both the Raiders and the Rams relocated elsewhere. However, a new stadium project, tentatively known as Los Angeles Stadium, was approved in 2009 with the expressed purpose of attracting an NFL team to the Los Angeles market.