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.
May Revolution
The Captaincy General of Chile followed a process analogous to that of the May Revolution, and elected a Government Junta that inaugurated the brief period known as "Patria Vieja". The Junta was defeated in 1814 at the Battle of Rancagua, and the subsequent Reconquista of Chile would make it a royalist stronghold once more. The Andes provided an effective natural barrier between the Argentine revolutionaries and Chile, so there was no military confrontation between them until the Crossing of the Andes, led by José de San Martín in 1817, a campaign that resulted in the defeat of the Chilean royalists.