Wikipedia - Mexican League

The Mexican League (Spanish: Liga Mexicana de Béisbol, LMB, lit.'Mexican League of Baseball') is a professional baseball league based in Mexico and the oldest running professional league in the country.

The league has 18 teams organized in two divisions, North and South. Teams play 114 games each season. Five teams in each division advance to a four-round postseason tournament that culminates in the Serie del Rey, a best-of-seven championship series between the two division champions. The Mexican League has two affiliated minor leagues, the Liga Norte de México and Mexican Academy League.

Though founded in 1925, the league joined the National Association of Professional Baseball Leagues (Minor League Baseball) in 1955, when it was designated a Double-A league. Some member teams entered player development contracts with teams in the National League at that time. Triple-A classification was granted in 1967. As part of the 2021 reorganization of the minors, the Mexican League was not included as a Triple-A league, though it continues to operate independently.