actions ensued in support of Madero who defeated the Mexican army in 1911 and who was elected president in a special election. Madero turned out to be a weak president and was overthrown in a coup d'état by Victoriano Huerta, head of the army, who installed himself as president in 1913. This led to the outbreak of the first civil war in which opposition to the dictator Huerta was led by Venustiano Carranza. Carranza's forces were called the "Constitutionalists" and captured Mexico City in 1914 and installed Carranza as president. Carranza, in turn, was opposed by Francisco Villa and Emiliano Zapata, leader of the Zapatistas, in the second civil war and eventually driven out of Mexico City in 1915. Carranza reluctantly incorporated many reforms in the Constitution of 1917, but the opposition to him continued. Militarily, the war ended in 1920 with the death of Carranza and the ascension to power of General Álvaro Obregón but coup attempts and sporadic uprisings continued throughout the next decade. Philatelically, this period resulted in numerous provisional and local stamps issued by the factions in control of different areas of the country. For example, in 1913-1914, the state of Sonora, controlled by the Madero forces, issued a series of typeset provisional issues, known as the "white" issue and the "green seal" issue. Sonora issued a typographed series of stamps known as the "Coach Seals" in 1914. The state of Oaxaca, maintaining a neutral position, similarly issued provisionals in 1915. In addition to the locals and provisionals, a great variety of overprints and surcharges were added to stocks of existing stamps by the powers then in control. Although many of these were printed on the stamps, they are commonly known by Mexican philatelists as "gomigrafos" or rubber stamps. Among the best known of these overprints are the "GCM" monograms, standing for "Gobierno Constitucionalista Mexicano" or the "Constitutional Mexican Government." Varieties of this overprint were first used by the Conventionalists supported by Villa, and later by the Constitutionalists and known as the Carranza overprints. Despite great disruption caused by the civil wars, opportunists took advantage of the strong interest in stamp collecting by producing for the philatelic market a number of forgeries of both the local issues as well as the overprints. In addition, many of the covers from this period were manufactured for collectors with the assistance of postal authorities and did not represent ordinary