(also called Marianas, formerly Ladrone Islands), group of 15 islands in Micronesia, Pacific Ocean, 1,500 mi (2,400 km) e. of Philippines; 450 sq mi (1,160 sq km); made Japanese mandate 1919 (except Guam, ceded to U.S. 1898); occupied by U.S. 1944; placed under U.S. trusteeship 1947; became commonwealth as Northern Marianas 1978; Covenant to Establish a Commonwealth with U.S. 1986, ending trusteeship; tourism, garment manufacturing, bonito fisheries; pop. 49,799