<P> The NFL was always the foremost professional football league in the United States; it nevertheless faced a large number of rival professional leagues through the 1930s and 1940s . Rival leagues included at least three separate American Football Leagues and the All - America Football Conference (AAFC), on top of various regional leagues of varying caliber . Three NFL teams trace their histories to these rival leagues, including the Los Angeles Rams (who came from a 1936 iteration of the American Football League), the Cleveland Browns and San Francisco 49ers (the last two of which came from the AAFC). By the 1950s, the NFL had an effective monopoly on professional football in the United States; its only competition in North America was the professional Canadian football circuit, which formally became the Canadian Football League (CFL) in 1958 . With Canadian football being a different football code than the American game, the CFL established a niche market in Canada and still survives as an independent league . </P> <P> A new professional league, the fourth American Football League (AFL), began play in 1960 . The upstart AFL began to challenge the established NFL in popularity, gaining lucrative television contracts and engaging in a bidding war with the NFL for free agents and draft picks . The two leagues announced a merger on June 8, 1966, to take full effect in 1970 . In the meantime, the leagues would hold a common draft and championship game . The game, the Super Bowl, was held four times before the merger, with the NFL winning Super Bowl I and Super Bowl II, and the AFL winning Super Bowl III and Super Bowl IV . After the league merged, it was reorganized into two conferences: the National Football Conference (NFC), consisting of most of the pre-merger NFL teams, and the American Football Conference (AFC), consisting of all of the AFL teams as well as three pre-merger NFL teams . </P> <P> Today, the NFL is considered the most popular sports league in North America; much of its growth is attributed to former Commissioner Pete Rozelle, who led the league from 1960 to 1989 . Overall annual attendance increased from three million at the beginning of his tenure to seventeen million by the end of his tenure, and 400 million viewers watched 1989's Super Bowl XXIII . The NFL established NFL Properties in 1963 . The league's licensing wing, NFL Properties earns the league billions of dollars annually; Rozelle's tenure also marked the creation of NFL Charities and a national partnership with United Way . Paul Tagliabue was elected as commissioner to succeed Rozelle; his seventeen - year tenure, which ended in 2006, was marked by large increases in television contracts and the addition of four expansion teams, as well as the introduction of league initiatives to increase the number of minorities in league and team management roles . The league's current Commissioner, Roger Goodell, has focused on reducing the number of illegal hits and making the sport safer, mainly through fining or suspending players who break rules . These actions are among many the NFL is taking to reduce concussions and improve player safety . </P> <P> From 1920 to 1934, the NFL did not have a set number of games for teams to play, instead setting a minimum . The league mandated a 12 - game regular season for each team beginning in 1935, later shortening this to 11 games in 1937 and 10 games in 1943, mainly due to World War II . After the war ended, the number of games returned to 11 games in 1946 and to 12 in 1947 . The NFL went to a 14 - game schedule in 1961, which it retained until switching to the current 16 - game schedule in 1978 . Proposals to increase the regular season to 18 games have been made, but have been rejected in labor negotiations with the National Football League Players Association (NFLPA). </P>

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