[6] In 1819, Francis O'Connor enlisted in the Latin American independence cause of Simon Bolivar, and sailed from Dublin with 100 officers and 101 men of the Irish Legion under the command of Colonel William Aylmer.

However, the Irish soldiers became demoralized by the cautious and inept conduct of the war by General Mariano Montilla and indiscipline evolved into mutiny.

Spanish General Canterac confessed to O'Connor after the battle that the choice of position made by the patriot army was a major factor in the defeat of the royalists.

[12][13] Furthermore, Bolívar would send O'Connor to make a survey of the Bolivian coast and determine which location was the best for Bolivia's main port of Cobija.

In 1828, O'Connor witnessed the events of that fateful year, namely the tragic ending of Pedro Blanco Soto, as he was in Sucre the night of the President's untimely assassination.

The Irishman writes the following account of the murder:There were rumors, of course, that General Blanco had been assassinated by the orders of the captain of the National Guard and that the first Chief of First Battalion, Colonel José Ballivian.

Lieutenant Colonel Prudencio Deheza, the same one who commanded the guard corps in the Recoleta convent of Chuquisaca the night of the cruel assassination of General Blanco, told me about that tragic event as follows: The order that was posted to the guards that day was: that in case of any attempt by the cholada [the indigenous popular masses of Bolivia] to rescue the prisoner, that he not be allowed to escape with his life.

This order was read to all the troops that made up the guard; and that same night, at midnight, the sentinel stationed in the corridor, sounded the alarm, and stated that groups of cholos were approaching the high wall in front of the convent.

The possibility of a Peruvian invasion and the souring of relations between Peru and Bolivia compelled President Andrés de Santa Cruz to recall O'Connor to active service.

Honoured, O'Connor remained in La Paz with the President and was given the position of Minister of War and Navy after José Miguel de Velasco took leave in July 1831.

Although needed in La Paz, O'Connor was dispatched by Santa Cruz to the Southern border with Argentina when the caudillo Facundo Quiroga threatened to invade and annex the Tarija Department, a region long considered to be Argentine by the citizens of that country.

Santa Cruz had wanted a death sentence for the colonel, however, when O'Connor ruled to fire Manrique from the army instead, a clash between the President and the Irishman took place.

Sensing an opportunity, since the enemy forces were marching in thin files and were not in a position to fight, O'Connor informed Santa Cruz who ordered an immediate attack.

A charge led by General Otto Philipp Braun effectively decided the outcome of the so-called Battle of Socabaya, ending in the capture and later execution of Salaverry and several of his officers.

O'Connor describes these as "the major blunders which cost Santa Cruz", the first being the anger of the army at the promotion of Calvo:Congress passed a law... which had Doctor Mariano Enrique Calvo, Prosecutor of the Supreme Court and then appointed Vice President of Bolivia, in charge of the Executive Power in the absence of General Santa Cruz, promoted to division general.

[17]The second major blunder which O'Connor describes is the annulment of the treaty with Chile signed under Salaverry, which had led to the declaration of war by said nation:[As for the war with Chile], the cause was the decree passed by General Santa Cruz which annulled the treaty of peace, friendship, and trade concluded between Salaverry, the intrusive president of Peru, and the Government of Chile... and the Captain General [Santa Cruz] knew it and must have weighed on him; however, he was so proud as a result of the victory at Socabaya that he imagined himself in a position to do whatever occurred to him at will, without looking at one side or the other, and this fact, which seemed insignificant to him, was the cause of his downfall and that of all the Confederation.

[20] After the treaty was signed, Santa Cruz negotiated with General Manuel Blanco Encalada the sale of all the horses in the Chilean Army in Arequipa, paying very high prices for the time.

O’Connor was sent hurriedly to Tarija alongside General Braun to prevent the Argentine army under Gregorio Paz from seizing the province.

O’Connor and Braun pursued Paz and eventually caught up to his army near the Montenegro mountain range, on the banks of the Bermejo River on 24 June 1838.

Although Paz's men were firing ferociously, the Bolivians under O’Connor led an impressive charge which resulted in the Argentine army abandoning their positions and fleeing to safety.

Previously, on 11 June, the second division of the Argentine army, led by Alejandro Heredia, was defeated at the Battle of Iruya, completely repelling the attack of the enemies.

Landing in Peru, the Restoration Army, composed of Peruvian exiles and Chileans, was able to crush Santa Cruz in the decisive Battle of Yungay, leading to the unravelling of the Confederation.

On 9 February 1839, General Velasco proclaimed himself against Santa Cruz, and in the following days the Departments of Chuquisaca, La Paz, and Cochabamba declared themselves in favour of the rebellion.

[23] O'Connor played a key role during the battles of Junin and Ayacucho, loyally serving Sucre and organizing with Santa Cruz what came to be among the fiercest and most well-trained armies in all of South America.