Revellers carry a photo of Cuban leader Fidel Castro during a May Day parade at Revolution Square in Havana, Cuba. Castro did not attend the annual celebration. May Day was inspired by a wave of strikes and demonstrations for a shorter work day, followed by the Haymarket Square killings during a labor dispute in Chicago in 1886. The Marxist International Socialist Congress adopted May Day as International Workers' Day at a meeting held in Paris in July 1889.
Sven Creutzmann/Mambo Photograph, Getty Images