Hawaii was a sovereign state until 1898, when a coup d’etat involving a group of businessmen, including several Americans, called on the U.S. to send in the Marines to protect their interests. It became a U.S. territory, then a state in 1959. Also in 1898, Guam and Puerto Rico were ceded to the U.S. from Spain after the American victory in the Spanish-American War. 

Has the U.S. had other real estate dealings with Denmark?