During the War of Reform (1858-1861), he was the principal general of the conservative army. He fought in the north and the central lowlands on the side of the conservatives, which had ousted the liberal regime of Benito Juárez, who had succeeded to the presidency of Mexico after the resignation of Comonfort. He was victorious in some early battles at Salamanca, Atentique, Ahualulco, but twice failed to take the liberal stronghold of Veracruz. He left the country after the conservative defeat, but played no part in the subsequent conservative efforts that brought Maximilian Hapsburg in the French Intervention in Mexico. Several presidents were appointed by different conservative factions. Miramón's faction eventually prevailed, and on February 2nd 1860, not yet 30 years old, he assumed the presidency in the zone controlled by the conservatives.