A few months later , the United States claimed ownership of the island as part of the Treaty of Paris of 1898 , which concluded the Spanish – American War , which they had won that year . On 19 February 1904 , the Union of Puerto Rico party became the first mass party to advocate for independence for Puerto Rico in the form of a sovereign nation . Other " independence parties " were formed in reaction to the colonial status of Puerto Rico with the United States . The Puerto Rican Nationalist Party , founded 17 September 1922 , also advocates independence . This party has since held that , by international law , the Spanish had no authority under the Treaty of Paris to cede the island , which was no longer theirs . The Nationalist movement attracted supporters following the repressions by the island government in the Ponce and the Río Piedras massacre . The profits generated by this one-sided arrangement were enormous , as US corporations developed large plantations
Ponce
Ponce massacre
Independence movement in Puerto Rico