May Revolution: Citizens of Buenos Aires expel Viceroy Baltasar Hidalgo de Cisneros during the "May Week", starting the Argentine War of Independence.

The May Revolution was a week-long series of events that took place from 18 to 25 May 1810, in Buenos Aires, capital of the Viceroyalty of the Río de la Plata. This Spanish colony included roughly the territories of present-day Argentina, Bolivia, Paraguay, Uruguay, and parts of Brazil. The result was the removal of Viceroy Baltasar Hidalgo de Cisneros and the establishment of a local government, the Primera Junta, on 25 May.

Buenos Aires, controlled by the government of the Autonomous City of Buenos Aires, is the capital and largest city of Argentina. It is located on the southwest of the Río de la Plata. Buenos Aires is classified as an Alpha− global city, according to the GaWC 2024 ranking. The city proper has a population of 3.1 million and its urban area 16.7 million, making it the twentieth largest metropolitan area in the world.

The Viceroyalty of the Río de la Plata or Viceroyalty of Buenos Aires meaning "River of the Silver", also called the "Viceroyalty of River Plate" in some scholarly writings, in southern South America, was the last to be organized and also the shortest-lived of one of the viceroyalties of the Spanish Empire in the Americas. The name "Provincias del Río de la Plata" was formally adopted in 1810 during the Cortes of Cádiz to designate the Viceroyalty of the Río de la Plata.

Baltasar Hidalgo de Cisneros y de la Torre was a Spanish Navy officer and colonial administrator. He took part in the Battle of Cape St Vincent and the Battle of Trafalgar, and in the Spanish resistance against Napoleon's invasion in 1808. He was later appointed Viceroy of the Viceroyalty of the Río de la Plata, replacing Santiago de Liniers. He disestablished the government Junta of Javier de Elío and quelled the Chuquisaca Revolution and the La Paz revolution. An open cabildo deposed him as viceroy during the May Revolution, but he attempted to be the president of the new government junta, thus retaining power. The popular unrest in Buenos Aires did not allow that, so he resigned. He was banished back to Spain shortly after that, and died in 1829.