The Viceroyalty of Río de la Plata was created in 1776 by King Carlos III, integrating within its jurisdiction the present territories of Argentina, Uruguay, Rio Grande do Sul and Santa Catarina current Brazil, Paraguay, Bolivia and northern Chile. The creation of the new Viceroyalty of Río de la Plata united Paraguay with the Viceroyalty of Peru. The capital of the new viceroyalty was in the city of Buenos Aires.
In 1782, the viceroyalty was established in the system of municipalities. Asunción was, in the Municipality or the Province of Paraguay, the only town with city status. The south area of the river Tebicuary and at east of the mountains of Caaguazú in turn corresponded to the Government of the Guarani missions (or Subordinated Province of Misiones) formed from the remains of the Jesuit missions that might come under Spanish control.
In 1806 and 1807 took place the British Invasions which occupied areas of the Viceroyalty of Río de la Plata of the Banda Oriental and much of Buenos Aires, and from Asuncion and Córdoba were sent troops to support the victory against the attackers.
In 1810 arrived in Buenos Aires the news that Spain had been occupied by French troops of Napoleon Bonaparte. Argentine patriots prepared the revolutionary movement. In Buenos Aires met in an open forum and established the Primera Junta (May 25th, 1810) in order to form a congress of all the provinces of the Viceroyalty of the Rio de la Plata, is the May Revolution. In 1810, due to the independent Primera Junta of Buenos Aires, the royal governor of Asunción, Bernardo de Velasco sent to Buenos Aires a note announcing the separation of the Province of Paraguay from the Viceroyalty of the Rio de La Plata, Velasco and his followers formed a meeting on June 24th, 1810, meeting in which they reiterated their loyalty to the Spanish monarchy of Ferdinand VII.
In 1811 troops under General Manuel Belgrano left on an expedition to liberate the Paraguay, but were defeated at the Battle of Tacuarí (March 9th, 1811) and at Paraguarí by local troops until then denominated as royalists. The victorious troops assumed a new identity and May 14th, 1811, revolutionary movement broke out Paraguayan military as directed by Captain Pedro Juan Caballero, Fulgencio Yegros, Vicente Ignacio Iturbe and Mauricio Jose Troche and politically by Fernando de la Mora Juana de Lara, Juan Valeriano and José Zeballos Gaspar Rodriguez de Francia, who intimated the Governor Velasco to join them. Zeballos and Francia then took a co-government with the Spanish official. Velasco would be removed within a month.
On June 17th, 1811 a congress appointed a governing board chaired by Fulgencio Yegros. Was established a confederation project between the United Provinces of Río de la Plata and Paraguay (including calling for the integration of Latin America), but the interests of elites of Buenos Aires and of Asuncion clashed despite the intentions of the patriots and of the people, such misunderstanding was encouraged by the United Kingdom of Portugal, Brazil and Algarve. On October 12th, 1811 was signed with the Buenos Aires envoy, General Manuel Belgrano, a Treaty of Friendship, Aid and Trade.
On November 25th, 1842 a congress formally declared the independence of Paraguay on the Argentina Confederation, it notified Rosas, who rejected it and was not recognized by Argentina untill July 17th, 1852.
