The Mexican first division (La Primera División de México ) was created by the Mexican Football Federation (Federación Mexicana de Fútbol Asociación) in 1943. The league was formed from Mexico's first professional league the Liga Mayor which contained ten teams, today's league has eighteen.
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The league is split into two seperate annual seasons, with the top teams competing at the end of each season in the playoffs to decide the overall champion. This wikipedia page and the official website have more information if you are interested.