The islands were sold by Spain to Germany in 1899 and
so remained under the German flag until the start of World
War One in 1914 when the Japanese moved against the
German administration in the islands and forced out.
Defeated Germany was stripped of all overseas possessions
at the end of the war in 1919.
The Mariana Islands were turned over to the newly created
league of nations to be administered as the Japanese Mandated
Territory. Japan had become an ally of the United States, Great
Britain and France shortly before the end of the war and was
named as the pacific area's administering authority.
By 1919 the islands were being administered Japan as a mandate
under the League of Nations.