May Revolution
The May Revolution was a direct reaction to Spain's Peninsular War. In 1808, King Ferdinand VII of Spain abdicated in favor of Napoleon, who granted the throne to his brother, Joseph Bonaparte. A Supreme Central Junta led resistance to Joseph's government and the French occupation of Spain, but eventually suffered a series of reversals that resulted in the Spanish loss of the northern half of the country. On February 1, 1810, French troops took Seville and gained control of most of Andalusia. The Supreme Junta retreated to Cadiz and dissolved itself, and the Council of Regency of Spain and the Indies replaced it. News of these events arrived in Buenos Aires on May 18, brought by British ships.
Montevideo
During the May Revolution of 1810 and the subsequent uprising of the provinces of Rio de la Plata, the Spanish colonial government moved to Montevideo. During that year and the next, Uruguayan revolutionary José Gervasio Artigas united with others from Buenos Aires against Spain. In 1811, the forces deployed by the Junta Grande of Buenos Aires and the gaucho forces led by Artigas started a siege of Montevideo, which had refused to obey the directives of the new authorities of the May Revolution. The siege was lifted at the end of that year, when the military situation started deteriorating in the Upper Peru region.