The APFA, by 1922 known as the National Football League, has remained the predominant professional football league in the United States, and, effectively, the entire world. The evolution from a haphazard collection of teams in big and small cities to the much more rigid structure it is in the present was gradual; the smaller markets were squeezed out in the late 1920s and early 1930s, a championship game was established in 1933, a draft was established in 1936, and schedules were standardized in the 1930s. A competing league has historically arisen to attempt to challenge the NFL's dominance every 10 to 15 years, but none managed to maintain long-term operations independent of the NFL and only two—the All-America Football Conference of the late 1940s and the American Football League of the 1960s—were strong enough to successfully compete against the league before the NFL subsumed their operations. Minor league football, although their leagues' memberships were unstable, began to arise in the late 1930s and remained viable as a business model up into the 1970s.
We have many A-Z keywords for this term. We offer them for FREE unlike many other keyword services, however we do require that you are a registered member to view them all so that the costs will remain lower for Us.
These are the linked keywords we found.
These are some of the images that we found within the public domain for your "Professional" keyword.