Complex sentence: The Rock Island Independents was one of the first professional American football teams, based in Rock Island, Illinois, in the National Football League from 1920 to 1925 and in the American Football League of 1926.
Split into simpler sentences: The Rock Island Independents was one of the first professional American football teams. They were based in Rock Island, Illinois, and played in the National Football League from 1920 to 1925 and in the American Football League of 1926.