Changes

During its existence it has merged with all or parts of three rival football leagues:

During its existence it has merged with all or parts of three rival football leagues:

*In 1937 the Cleveland Rams -- now the [[Los Angeles Rams]] -- switched from the American Football League (no relation to the 1960's league of the same name) to the NFL.

*In 1937 the Cleveland Rams -- now the [[Los Angeles Rams]] -- switched from the American Football League (no relation to the 1960's league of the same name) to the NFL.

*In 1950 it absorbed three teams from the All-America Football Conference (the [[Cleveland Browns]], the [[San Francisco 49ers]], and a team called the Baltimore Colts which is not related to the current franchise called the [[Indianapolis Colts]]).

*In 1950 it absorbed three teams from the All-America Football Conference (the [[Cleveland Browns]], the [[San Francisco 49ers]], and a team called the Baltimore Colts which is not related to the current franchise called the [[Indianapolis Colts]], that team folded within two seasons).

*In 1970 it merged with the American Football League, which began operations in 1960.  As part of the merger agreement, beginning in 1967 it hosted a championship game between the leagues, which is now today's [[Super Bowl]].  Also, in order to equalize the number of teams between what would be the [[National Football Conference]] (comprised of NFL teams) and the [[American Football Conference]] (comprised of AFL teams), three NFL teams -- the Browns, the Colts and the [[Pittsburgh Steelers]] -- were moved to the AFC.

*In 1970 it merged with the American Football League, which began operations in 1960.  As part of the merger agreement, beginning in 1967 it hosted a championship game between the leagues, which is now today's [[Super Bowl]].  Also, in order to equalize the number of teams between what would be the [[National Football Conference]] (comprised of NFL teams) and the [[American Football Conference]] (comprised of AFL teams), three NFL teams -- the Browns, the Colts and the [[Pittsburgh Steelers]] -- were moved to the AFC.

Otherwise, the league has grown through expansions into new markets, which has proven tremendously successful: as an example it expanded into [[Dallas]] in 1960 with the [[Dallas Cowboys]] franchise, which is the league's most valuable and among the most valuable of all sports franchises worldwide.  It is also very active in teams relocating to other markets (and sometimes returning, such as the [[Los Angeles Rams|Rams franchise]] moving from Cleveland to Los Angeles, then moving to St. Louis and then returning back to Los Angeles).

Otherwise, the league has grown through expansions into new markets, which has proven tremendously successful: as an example it expanded into [[Dallas]] in 1960 with the [[Dallas Cowboys]] franchise, which is the league's most valuable and among the most valuable of all sports franchises worldwide.  It is also very active in teams relocating to other markets (and sometimes returning, such as the [[Los Angeles Rams|Rams franchise]] moving from Cleveland to Los Angeles, then moving to St. Louis and then returning back to Los Angeles).