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 Day riots of 1919
The previous year, Eugene Debs's Federal Court trial was held in Cleveland, and Charles Ruthenberg's Socialist Party chose to hold a march which would both protest Debs' imprisonment as well as help promote Ruthenberg's own candidacy for mayor of Cleveland. The procession consisted of 32 groups divided into four units, each holding a Socialist flag and an American flag at its head. Although the cause of the riots is disputed, repeated demands by the police and army personnel that the marchers relinquish their flags reportedly became a flashpoint.