There are five major reasons that professional sports expanded across the North American continent in the decades after World War II.
- The expansion of the nation’s transportation infrastructure, namely highways and air travel.
- The postwar affluence of the nation, especially in the rapidly expanding suburbs.
- The emergence of cities in the South and West capable of supporting professional sports franchises.
- The monopoly status of professional sports leagues, which were protected by all kinds of anti-trust exemptions, enabling the big leagues to dictate the terms of league expansions.
- The emergence of sports as a signifier of national prominence.