Professional team sports in the United States have a long history, starting with baseball in the 1860s. Leagues like the National League set rules for teams and players, but also had discriminatory practices like barring African Americans. Over time, other major leagues like the NFL and NBA emerged, facing challenges like franchise relocations and player salaries. After World War II, professional sports became more popular, with athletes now earning over $2 million a year on average. The NFL became the most successful league, surpassing baseball in popularity in the 1970s.