The Mexican Army (Spanish: Ejército Mexicano) is the combined land and air branch and largest of the Mexican Military services; it also is known as the National Defense Army. It is famous for having been the first army to adopt and use an automatic rifle, (the Mondragón rifle), in 1899, and the first to issue automatic weapons as standard issue weapons, in 1908. The Mexican Army has an active duty force of 470,000 (2012 est.).

Mexico has no foreign nation-state adversaries and little ambition to impose itself upon other nations. It repudiates the use of force to settle disputes and rejects interference by one nation in the affairs of another. Although it has not suffered a major terrorist incident, Mexico considers itself a potential target for international terrorism.

In the prehispanic era there lived many indigenous tribes and highly developed city-states in what is now known as central Mexico. The most advanced and powerful kingdoms were those of Tenochtitlan, Texcoco and Tlacopan which comprised populations of the same ethnic origin and were politically linked by an alliance known as the Triple Alliance; colloquially these three states are known as the Aztec. They had a center for higher education called the Calmecac in Nahuatl, this was where the children of the Aztec priesthood and nobility receive rigorous religious and military training and conveyed the highest knowledge such as: doctrines, divine songs, the science of interpreting codices, calendar skills, memorization of texts, etc. In Aztec society it was compulsory for all young male nobles, as well as commoners, to form part of the armed forces beginning at the age of 15.