1900 (May 16) longer plain envelope to Presidente de la honorable Junta at San Juan bearing USA 2 cent overprinted Porto Rico (Scott 211) tied Arecibo Sta./Porto Rico duplex date stamp & on reverse San Juan P.R. (16 May) arrival cds…………….
In 1898, during the Spanish–American War, Puerto Rico was invaded and subsequently became a possession of the United States. The first years of the 20th century were marked by the struggle to obtain greater democratic rights from the United States. The Foraker Act of 1900, which established a civil government, and the Jones Act of 1917, which made Puerto Ricans U.S. citizens, paved the way for the drafting of Puerto Rico’s Constitution and its approval by Congress and Puerto Rican voters in 1952. However, the political status of Puerto Rico, a Commonwealth controlled by the United States, remains an anomaly…https://en.wikipedia.org/wiki/History_of_Puerto_Rico