Rival Leagues to the National Football League have existed since the 1920s, most of them from the 1920s to 1960s called themselves the American Football League, and since then there has been a variety of names and ideas, such as the World Football League (1974-1975), Spring Leagues (United States Football League, 1983-1985), Indoor Football Leagues (Arena Football League 1986-present, though a Minor League rather than a Major League rival since 2000), Extreme Leagues (XFL 2001), Leagues aimed at the Drinks market (Lingerie / Legends Football Leagues 2004-Present).
Only the American Football League of 1960-1969 has been successful long-term, leading to both the start of the Super Bowl between the AFL Winners and the NFL Winners in 1967 and the eventual merger of the two leagues (They are now the American & National Football Conferences in the NFL – the Super Bowl is still played between the winners of the two Conferences)
American Football League Era (1920-1949):
World / Continental Leagues Era (1940-present):
Spring / Reduced Numbers Leagues Era (1986-2019)
AAA / Development Leagues (1991-2019):
Minority Football Leagues (2020-):