The American Professional Football Association (APFA) lasted all of 2 years and was replaced by what is now the National Football League. Twelve teams were in the APFA, that is if you want to count the Muncie Flyers, who played but 1 game, and the league boasted several more the following year- but very few played a "full" schedule.
In 1922, the newly formed NFL comprised of 18 teams – a number that expanded and contracted often in the next 10 years. Despite the title, there was not much “national” to the league. Rock Island (IL) was the farthest west of the 18, and Louisville, KY, was NFL’s southern-most team.
University of Illinois star Red Grange put the NFL on the sports map in the mid 1920's, but by the early 1930's, the game was boring - lots of ties (lots of 0-0 ties!) and needed a few major changes. The catalyst for these changes came after the 1932 championship game (played indoors!) between George Halas' Chicago Bears and the Portsmouth Spartans (now the Detroit Lions). Check out the game and the changes that followed!