Otto Philipp Braun, General Felipe Braun, was German in origin. In 1820 he joined the army of
Simón Bolívar during the
Spanish American wars of independence, rising to a senior position. He entered the service of Bolivian President
Andrés de Santa Cruz in 1830. As a Divisional General he accompanied Santa Cruz in the June 1835 invasion of Peru, in which the Bolivia-Peru Confederation was formed. He was to lead the Bolivian troops to victory at Montenegro. Francis O'Connor was an Irish volunteer who became Bolívar's chief of staff in the "United Army of Liberation in Peru". In 1826 he was appointed military governor of the
Bolivian town of
Tarija.
Juan Manuel de Rosas was effective ruler of Argentina from 1829 until 1852. In 1837 Rosas entered an alliance with Chile against the confederation of Peru and Bolivia, declaring war on 19 May 1837. His motives were mixed, but the main one was a territorial dispute concerning the
Province of Tarija. Another factor was the support given by Santa Cruz to Rosas' domestic enemies, the Unitarian faction. In the initial fighting, the Bolivians under General Felipe Braun entered Argentina and had a series of minor successes. Later in 1837 the Bolivians withdrew to their side of the border after a defeat at
Humahuaca. The Argentine forces were unable to follow up until they had dealt with the defection of the militia of
Jujuy Province and with uprisings by Unitarian rebels, and had obtained reinforcements. In April 1838 the Argentines, with 1,000 men, invaded Bolivia and won minor engagements at Acambuco on 27 April, Zapatera on 2 May and Pajonal on 6 May. Argentine forces under Colonel
Gregorio Paz moved to the San Luis valley near Tarija, arriving there on 10 June 1838. According to an Argentine account, Paz was told by the border commander that General Braun had reached Tarija with a force of five hundred infantry and 50 cavalry. He was also told that the people of Tarija would support the Argentines. Based on this information, Paz decided to advance to the town of Tarija. By 24 June 1838 he was within of his goal. The Bolivians took a stand at Montenegro hill. ==Battle==