May Revolution
The mutiny of Aranjuez in 1808 led King Charles IV of Spain to abdicate in favor of his son, Ferdinand VII. Charles IV requested that Napoleon restore him to the throne; instead, Napoleon crowned his own brother, Joseph Bonaparte, as the new Spanish King. These events are known as the Abdications of Bayonne. Joseph's coronation was met with severe resistance in Spain, which started the Peninsular War, and the Supreme Central Junta took power in the name of the absent king. This also led to Spain switching allegiances from France to Britain. France eventually invaded Sevilla, and a Council of Regency based in Cadiz replaced the disbanded Supreme Central Junta.
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.