is that Mexico is a so called "civil law" country while the U.S. is a "common law" country.
Mexico's civil law system is derived primarily from Roman law as set forth in the compilation of codes and statutes of the Emperor Justinian, called Corpus Juris Civilis, and later refined in the French or Napoleonic Code of 1804.
Mexico's legal system is also influenced by colonial law (the Spanish and "Indian" law of Spain's colonization in the areas that became Mexico and other present day Latin American countries),