Being a former Spanish and then German territory, Saipan became a Mandate of Japan by the League of Nations after World War I, and thus, a large number of Japanese civilians lived there — at least 25,000.
Sebagai wilayah bekas Spanyol dan kemudian Jerman, Liga Bangsa Bangsa menjadikan Saipan wilayah mandat Jepang setelah Perang Dunia Pertama, sehingga banyak sekali penduduk sipil Jepang di sana, sekitar 25.000.