Guam was seized by America.
Guam ( [ ˈɡwɑːm ] or [ ˈɡwɒm ] Chamorro : Guåhån [ ˈɡʷɑhɑn ] formally the Territory of Guam ) is an unincorporated and organized territory of the United States . During the Spanish -- American War , the United States captured Guam on June 21 , 1898 . Under the Treaty of Paris , Spain ceded Guam to the United States on December 10 , 1898 . Guam is among the seventeen Non-Self-Governing Territories of the United Nations . Guam endured hostilities when American forces recaptured the island on July 21 , 1944 ; Liberation Day commemorates the victory .