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.
Historiography of the May Revolution
On the other hand, the Congress of Tucuman issued a manifest in 1817, more than a year after the declaration of independence. It detailed abuses made by the Spanish, and former chances for separatism that were not used. Of course, once the independence was declared openly, there would not have been any further need for keeping a masquerade of submission. In the specific case of the May Revolution, it says: