The Mexican Army () is the combined land and air branch and is the largest part of the Mexican Armed Forces; it is also known as the National Defense Army. The Army is under the authority of the Secretariat of National Defense or SEDENA and is headed by the Secretary of National Defence. It was the first army to adopt (1908) and use (1910) a self-loading rifle, the Mondragón rifle. The Mexican Army has an active duty force of 198,000 with 76,000 men and women of military service age. History Antecedents Pre-Columbian era: native warriors In the prehispanic era, there were 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 males, nobles as well as commoners, to join part of the armed forces at the age of 15. Recruited by regional and clan groups (calpulli) the conscripts were organized in units of about 8,000 men (Xiquipilli). These were broken down into 400 strong sub-units. Aztec nobility (some of whom were the children of commoners who had distinguished themselves in battle) led their own serfs on campaign. Itzcoatl "Obsidian Serpent" (1381–1440), fourth king of Tenochtitlán, organized the army that defeated the Tepanec of Atzcapotzalco, freeing his people from their dominion. His reign began with the rise of what would become the largest empire in Mesoamerica. Then Moctezuma Ilhuicamina "The arrow to the sky" (1440–1469) came to extend the domain and the influence of the monarchy of Tenochtitlán. He began to organize trade to the outside regions of the Valley of Mexico. This was the Mexica ruler who organized the alliance with the lordships of Texcoco and Tlacopan to form the Triple Alliance. The Aztec established the Flower Wars as a form of worship; these, unlike the wars of conquest, were aimed at obtaining prisoners