The Puerto Rican Nationalist Party was founded in 1922 . It strongly criticized the American colonial regime for its menace to the Spanish and Latin American roots of the Puerto Rican culture . It also advocated for complete independence . The PNP began to grow with the leadership of Dr. Pedro Albizu Campos , who was later jailed by the colonial regime under charges as a subversive leader . On March 21 , 1937 , a peaceful march was organized in the southern city of Ponce by the nationalists after receiving authorization from the pertinent authorities . The march was organized to commemorate the abolition of slavery and to demand the release of Albizu Campos from federal prison . The permit , however , was revoked by the U.S.-appointed governor of the Island Blanton Winship minutes before the march was to start . The march turned into a bloody event when the Insular Police ( " a force somewhat resembling the National Guard of the typical U.S. state " and which answered to governor Winship ) opened fire upon , what a U.S. Congressman and others reported were unarmed and defenseless cadets and bystanders alike killing 19 and badly wounding over 200 more , many in their backs while running away . It came to be known as the Ponce massacre
Ponce massacre
Ponce massacre
Politics of Puerto Rico