|Part of Spanish American wars of independence|
The Argentine armies crossing the Paraná river
|United Provinces of the Río de la Plata||Royalist Paraguay|
|Commanders and leaders|
|Manuel Belgrano||Bernardo de Velazco|
The Paraguay campaign (1810–1811) was the attempt by a Buenos Aires sponsored militia, commanded by Manuel Belgrano, to win the Intendency of Paraguay for the revolutionary cause. The first battle was fought in Campichuelo and the Argentines claimed victory. However, they were completely vanquished in the subsequent battles of Paraguarí and Tacuarí. Although the campaign ended in a military failure, Paraguay broke its links with the Spanish crown just two months after Belgrano's withdrawal.
Three months after the creation of the Primera Junta, Manuel Belgrano was appointed Chief Commander of an army destined to gather support at Corrientes, Santa Fe, Paraguay and the Banda Oriental. Few days later his goal is made more specific: he must aim for Paraguay. The Junta had been informed that the patriotic party was strong, and a small army would suffice to take control. Trusting such information, Belgrano was destined for Paraguay with two possible goals, get acknowledgment for the Junta in Paraguay or promote a new government that would stay in friendly terms with Buenos Aires. Belgrano ignored by then that on July 24 a general assembly discussed about the Junta of Buenos Aires, and decided to reject it and pledge allegiance to the Regency Council of Spain. There were three main political tendencies in Paraguay: those who supported the Regency Council, those who supported the Junta of Buenos Aires, and those who supported a declaration of independence. Paraguay had been a highly isolated region during the colonial times, which made the independentist ideas stronger than in other regions of the Spanish viceroyalties.
Belgrano headed for the north with nearly two hundred men, expecting to gather more people on his way to the Paraná River. Soldiers from the Blandengues regiments of San Nicolás and Santa Fe joined them en route, and later the Junta sent reinforcements of other two hundred soldiers. The army was welcomed by most of the population found in their way, receiving donations and new recruits in most villages. Finally, the army gathered was composed of nearly 950 men, among infantry and cavalry, divided in four divisions with one piece of artillery each.
By the end of October the army stopped at 
From that point the army moves to Candelaria, which is used as stronghold for the attack on Paraguay. The terrain of the zone gave a clear advantage to Velazco, who confronted Belgrano: the Paraná River, nearly 1,000 m. wide, was an effective natural barrier, and once it was crossed the patriotic army would have to move for a long distance across a land without supplies. Swamps, hills, rivers and lakes would also force the army to march slowly, making a possible retreat very difficult. The Parana was crossed with several boats on December 19, and a force of 54 Paraguayan soldiers was forced to flee during the battle of Campichuelo. Belgrano saw Velazco's army from the Mbaé hill, and despite being greatly outnumbered he ordered the attack anyway, trusting in the moral strength of his soldiers. When the battle of Paraguarí started patriots had briefly the upper hand, but eventually Velazco made his numeric superiority prevail. Even with 10 deaths and 120 soldiers taken prisoner, Belgrano wanted to keep on fighting, but his officers convinced him to retreat.
The army left for Tacuarí, being closely watched by the combined armies of 
The Paraguay campaign was a complete defeat for the Primera Junta from a military point of view, but it wasn't a complete political failure: probably because of it, Paraguay started to consider independence and by May 14 they declared independence from Spain. However, in doing so they also break up with Buenos Aires: they maintained good relations, but were no longer part of the same political entity.
- Luna, p. 60
- Instituto Nacional Belgraniano – Campaña al Paraguay
- Luna, p. 63
- Luna, p. 65
- Luna, p. 68
- Luna, p. 72