The Virgin Islands are the western island group of the Leeward Islands, which are the northern part of the Lesser Antilles, and form the border between the Caribbean Sea and the Atlantic Ocean. Politically, the eastern islands form the British Virgin Islands and the western ones form the United States Virgin Islands. The British Virgin Islands is an overseas territory of the United Kingdom comprising Tortola, Virgin Gorda, Jost Van Dyke and Anegada. The U.S. Virgin Islands is an unincorporated organized territory of the United States comprising St. Croix, St. John, St. Thomas and Water Island. The Virgin Passage separates the U.S. Virgin Islands from the Spanish Virgin Islands of Vieques and Culebra, which are part of Puerto Rico. The United States dollar is the official currency on both the British and U.S. Virgin Islands as well as the Spanish/Puerto Rican Virgin Islands. Christopher Columbus named the islands after Saint Ursula and the 11,000 Virgins (Spanish: Santa Ursula y las Once Mil Vírgenes), shortened to the Virgins (las Vírgenes). The official name of the British territory is the Virgin Islands, and the official name of the U.S. territory is the Virgin Islands of the United States. In practice, the two island groups are almost universally referred to as the British Virgin Islands and the U.S. Virgin Islands. The Virgin Islands were originally inhabited by the Arawak, Carib, and Cermic, all of whom perished during the colonial period through enslavement, foreign disease, and mass suicide. The islands got their current name after Christopher Columbus named the islands Santa Ursula y las Once Mil Vírgenes, shortened to Las Vírgenes, after the legend of Saint Ursula and her 11,000 virgins. European colonists later settled here and established sugar plantations, at least one tobacco plantation, and purchased slaves acquired from Africa. The plantations are gone, but the descendants of the slaves remain the bulk of the population, sharing a common African-Caribbean heritage with the rest of the English-speaking Caribbean. In 1916 and 1917, Denmark and the U.S., respectively, ratified a treaty in which Denmark sold the Danish West Indies to the United States of America for $25 million in gold. In the 1990s a Puerto Rican tourism campaign renamed the Passage Islands as the Spanish Virgin Islands, though they are seldom[clarification needed] identified as such on maps and atlases. They are part of the Commonwealth of Puerto Rico, located east of the main island of Puerto Rico. However, they are geographically part of the Virgin Islands chain. They are closer to St. Thomas than St. Thomas is to St. Croix.