The Ponce massacre was an event that took place on Palm Sunday, March 21, 1937, in Ponce, Puerto Rico, when a peaceful civilian march turned into a police shooting that killed 21 Puerto Ricans and wounded over 200 others. Most of the killed where shot in their backs. The march had been organized by the Puerto Rican Nationalist Party to commemorate the abolition of slavery in Puerto Rico by the governing Spanish National Assembly in 1873 and to protest the U.S.