Association of Professional Football Leagues

The Association of Professional Football Leagues was a compact formed in 1946 among the National Football League and three minor leagues of professional American football: the American Association (which subsequently changed its name to the American Football League), the Dixie League, and the Pacific Coast Professional Football League. While the NFL had an informal farm system in the pre-World War II AA, this was the first time in which it had a working arrangement with multiple leagues whose local popularity rivaled that of the major league.

Source: Wikipedia — Association of Professional Football Leagues (CC BY-SA 4.0)