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.
Juan José Castelli
When the news of the fall of the Junta of Seville arrived, the group headed by Castelli and Belgrano led the process leading to the May Revolution. Castelli and Saavedra were the most important leaders of the time, and first discarded Martín Rodríguez's plan to expel Cisneros in a coup d'état. After several discussions, they decided to request an open cabildo, an emergency popular assembly. Castelli and Belgrano negotiated with the senior alcalde and nobleman, Juan de Lezica, and the procurator, Julián de Leiva. Although they convinced them, they still needed the permission of Cisneros himself, for which Castelli and Rodriguez went to his office at the Fort of Buenos Aires. Previously, Cornelio Saavedra had denied Cisneros the support of the Regiment of Patricians, on the premise that with the disappearance of the Junta of Seville—who had appointed him as viceroy—he no longer had the right to hold that position.