The Viceroyalty of the Río de la Plata (Spanish: Virreinato del Río de la Plata, also called Viceroyalty of the River Plate in some scholarly writings) was the last to be organized and also the shortest-lived of the Viceroyalties of the Spanish Empire in the Americas.
The Viceroyalty was established in 1776 from several former Viceroyalty of Perú dependencies that mainly extended over the Río de la Plata Basin, roughly the present-day territories of Argentina, Chile, Bolivia, Paraguay and Uruguay, extending inland from the Atlantic Coast. The colony of Spanish Guinea (present-day Equatorial Guinea) also depended administratively on the Viceroyalty of Rio de la Plata. Buenos Aires, located on the western shore of the Río de la Plata estuary flowing into the Atlantic Ocean, opposite the Portuguese outpost of Colonia del Sacramento, was chosen as the capital. Usually considered one of the late Bourbon Reforms, the organization of this viceroyalty was motivated on both commercial grounds (Buenos Aires was by then a major spot for illegal trade), as well as on security concerns brought about by the growing interest of competing foreign powers in the area. The Spanish Crown wanted to protect its territory against Great Britain and the Kingdom of Portugal.
But these Enlightenment reforms proved counterproductive, or perhaps too late, to quell the colonies' demands. The entire history of this Viceroyalty was marked by growing domestic unrest and political instability. Between 1780 and 1782, the Rebellion of Túpac Amaru II inspired a violent Aymara-led revolt across the Upper Peru highlands, demonstrating the great resentment against colonial authorities by both the mestizo and indigenous populations. Twenty-five years later, the Criollos, native-born people of the colony, successfully defended against two successive British attempts to conquer Buenos Aires and Montevideo. This enhanced their sense of autonomy and power at a time when Spanish troops were unable to help.
In 1809, the Criollo elite revolted against colonial authorities at La Paz and Chuquisaca, establishing revolutionary governments, juntas. Although short-lived, these provided a theoretical basis for the legitimacy of the locally based governments, which proved decisive at the 1810 May Revolution events deposing Viceroy Cisneros at Buenos Aires.
The revolution spread across the Viceroyalty, except for Paraguay (which declared itself an independent nation in 1811) and Upper Peru (which remained controlled by royalist troops from Lima, and was eventually re-incorporated into the Viceroyalty of Peru). Meanwhile, the Governor of Montevideo Francisco Javier de Elío, appointed as a new Viceroy by the Cortes of Cádiz in 1811, declared the Buenos Aires Junta seditious. However, after being defeated at Las Piedras, he retained control only of Colonia del Sacramento and Montevideo. He departed by ship to Spain on 18 November and resigned as Viceroy in January 1812. By 1814, as the revolutionary patriots entered Montevideo, following a two-year-long siege, the Viceroyalty was finished as government of the region.