Why did two baseball leagues form?
The commissioner and creator of baseball, in the time Major League Baseball was organized, wanted the championship to be decided by the top teams in each league. So, they created the American League and National League. The winner of each league faces each other in the World Series to decide the champion.
The National League was founded in 1876. The American League was founded in 1901. At first, the two leagues were enemies. The American League 'stole' a lot of players from the National League by offering them more money. After two years, the two leagues made a truce and became friends, so to speak. They decided to stay as two separate leagues instead of merging into one.