Since I originally posted I’ve been doing some checking. They played other local clubs and traditional rivals – arranging dates and fixtures themselves. In fact, in English Rugby Union (strictly amateur until 1995) this was the situation until 1987!
From the English Football League website, the League was formed when the professional clubs (all in the north of England) realised that “football had become a disorganised shambles with games constantly being called off because clubs had arranged more lucrative matches elsewhere.” What surprised me looking at the NFL web site was the this was almost the same pattern as occurred in the States with the formation of the original State leagues and the American Professional Football Association (the fore-runner of the NFL) in 1920. It isn’t clear looking at the sites is why they evolved so differently, both in terms of promotion/relegation and relative power of the league v the clubs.
Reading their histories I can speculate (in other words make WAGs ) that the shear size of the USA had something to do with the setting up of geographical Divisions rather than two or more national Divisions with promotion between them as the number of clubs in the league increased. Until air travel became common and the clubs richer it would hardly be practical to have truly national First and Second Divisions whereas even at the start of the twentieth centuary trains will get you anywhere in Engand in a few hours. Even so, the English Football League had a Third Division (North) and a Third Division (South) for a while between the Wars. On the relative power of clubs v the leagues I wonder if it could be something to do with the much earlier introduction of large amounts of TV cash into the game combined with competion between two rival leagues that required the clubs to cooperate more?
On the wider question, do any American sports have leagues with promotion/relegation?