The NFL was always the largest professional football league in the United States; it nevertheless faced numerous 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.