 The UNS was founded in May 1937, during the leftist administration of President Lázaro Cárdenas (1934–40), by a group of Catholic political activists led by José Antonio Urquiza, who was murdered in April 1938.It was a revival of the Catholic reaction that drove the Cristero War (that ended in 1929), and its core was centered in the Bajío rural bourgeoisie and professional lower middle-class, where Catholicism was very strong.The group published the "Sinarquista Manifesto," opposing the policies of the government of President Lázaro Cárdenas.