1) The Negro Baseball Leagues were formed in the late 1800s after black baseball players were excluded from the major and minor baseball leagues.
2) Throughout the early 1900s, black baseball players faced significant discrimination and were not allowed to play in the major leagues. They formed their own successful Negro Leagues that drew large crowds.
3) After World War II, baseball commissioner Happy Chandler said black players should be allowed to play if they could serve in the war. This opened the door for Jackie Robinson to sign with the Brooklyn Dodgers in 1947, integrating major league baseball.