a bloody February 1913 coup. Forces opposed to the Huerta regime united against him, particularly the Constitutionalists in the north. These were led by a civilian, Venustiano Carranza as "First Chief," commanding forces led by a number of generals, but most prominently Alvaro Obregón and Pancho Villa. In the Morelos region, an intense guerrilla warfare was waged by forces led by Emiliano Zapata. The Federal Army supporting Huerta was defeated at the Battle of Zacatecas and finally disbanded in 1914 and a new Government army was created from Obregón's Constitutionalist forces. Zapata was assassinated in 1919; Villa was bought off and took up civilian life in northern Mexico, before being assassinated in 1923. During the post-military phase following 1920, a number of Constitutionalist leaders became presidents of Mexico: Alvaro Obregón (1920–1924), Plutarco Elías Calles (1924–28), Lázaro Cárdenas (1934–1940), and Manuel Avila Camacho (1940–1946). When Lázaro Cárdenas reorganized the political party founded by Plutarco Elías Calles, he created sectoral representation of groups in Mexico, one of which was the Mexican Army. In the subsequent reorganization of the party, which took place in 1946, the Institutional Revolutionary Party no longer had a separate sector for the army. No military man has been president of Mexico after 1946. Contemporary era Post-revolutionary period The ending of the Diaz regime saw a resurgence of numerous local forces led by revolutionary generals. In 1920, more than 80,000 Mexicans were under arms, with only a minority forming part of regular forces obedient to a central authority. During the 1920s, the new government demobilised the revolutionary bands, reopened the Colegio Militar (Military Academy), established the Escuela Superior de Guerra (Staff College), and raised the salaries and improved the conditions of service of the rank and file of the regular army. In spite of an abortive generals' revolt in 1927, the result was a professional army obedient to the central government. During this period the army was reduced in numbers through the disbandment of twenty mounted cavalry regiments, ten infantry battalions and the majority of the specialist railroad units previously required. In 1937 a process of accelerated modernisation began with the creation of companies of light tanks, mechanised infantry and motorised anti-aircraft batteries. During the 1930s, the political role of the officer corps was reduced by the governing Revolutionary Party and a workers' militia was established, outnumbering the regular army by two to one. By the end of World