The Union of Puerto Rico (Spanish: Unión de Puerto Rico, UPR), also known as the Unionist Party (Spanish: Partido Unionista, PU), was a major political party in Puerto Rico in the early 20th century. The Union of Puerto Rico was known as the dominant political party of the island from 1904 to 1932. UPR founder Luis Muñoz Rivera also founded La Democracia, which effectively acted as the UPR publication. 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.