1940 American Football League season
The 1940 AFL season was the first season of the third American Football League. The league was formed when the New York Yankees, Boston Bears, and Buffalo Indians were joined by the Cincinnati Bengals, Columbus Bullies, and Milwaukee Chiefs of the minor American Professional Football Association (the mass defection doomed the minor league).
Source: Wikipedia — 1940 American Football League season (CC BY-SA 4.0)