Major League owners decide to return to playing an unbalanced schedule (teams play more games against teams in their own division) rather than the presently-used balanced schedule in which they play approximately the same number of games against all teams within the league. The American League has used a balanced schedule since 1977 and the National League started in 1993.

This Day In Baseball

On July 14, 2000 Major League owners decide to return to playing an unbalanced schedule (teams play more games against teams in their own division) rather than the presently-used balanced schedule in which they play approximately the same number of games against all teams within the league. The American League has used a balanced schedule since 1977 and the National League started in 1993.

Source
Baseball Reference July 14