The National Football League may have been founded in 1920, but it's roots span all the way back to 1892 when former Yale All-American guard William Heffelfinger was paid $500 by the Allegheny Athletic Association to play in a game against the Pittsburgh Athletic Club. This made him the first ever professional football player. Yet it would take another eighteen years for American football to achieve a league of any real organization.
The American Professional Football Association was formed on September 17, 1920 and included ten teams from four different states. Yet the APFA only lasted two seasons before it was reorganized into the National Football League on June 24, 1922.
Only two teams currently in the NFL are founding members - the Chicago Bears (formally the Decatur Staleys) and the Arizona Cardinals (formally the Chicago Cardinals). The Green Bay Packers is the oldest NFL franchise to stay in operation with the same name in the same location (they were founded in 1919 but didn't join the NFL until 1921).
Early championships were awarded on a win-loss record alone, which was rather haphazard considering the teams didn't all play the same amount of games, and some played against non-league teams.
In 1958, the Baltimore Colts and New York Giants played for the championship in what has become known as 'The Greatest Game Ever Played'. It was the first NFL playoff game to go into sudden death overtime. The game marked the beginning of the NFL's popularity surge, and eventual rise to the top of the United States sports market. A major reason was that the game was televised across the nation by NBC. Baltimore receiver Raymond Berry recorded 12 receptions for 178 yards and a touchdown. His 12 receptions are a championship record that still stands today.
The rival American Football League, founded in 1960, was also very successful and the NFL decided to merge with them in 1970 instead of continue competing against them, which would also put an end to player poaching. The merger not only resulted in an expanded league but also the creation of the Super Bowl-which has become the most-watched annual sporting event in the United States. The league continued to expand to its current size of 32 teams. Although the AFL was subsumed by the NFL, many of the league's innovations were later adapted by the NFL and it became the game we all know and love.
The NFL solidified its dominance as America's most popular spectator sport in the 1970s. The Super Bowl became an unofficial holiday and the top-rated TV program more years than not. The introduction of Monday Night Football brought in big ratings with its blend of sports and entertainment. Both of these events are still going strong today.
Many other leagues have attempted to form other the years, trying to capitalize on the NFL's success, but none have succeeded in reaching any level of competition comparable to the NFL.