The American League developed from the Western League, a minor league based in the Great Lakes states, which eventually aspired to major league status. It is often called the Junior Circuit because it claimed Major League status for the 1901 season, 25 years after the formation of the National League (the "Senior Circuit"). Since 1903, at the end of every season, the American League champion plays in the World Series against the National League champion.
For the first 96 years, American League teams faced their National League counterparts only in exhibition games or in the World Series. Beginning in 1997, interleague games have been played during the regular season and count in the standings. As part of the agreement instituting interleague play, the designated-hitter rule is used only in games where the American League team is the home team.