In the 1930s, many Japanese citizens, seeking new opportunities, emigrated to the South Sea Mandate, known as Nan’Yō. Soon the Japanese population of these islands grew to outnumber the islanders. Ultimately, it was only the catastrophic outcome of the Pacific War that reversed this trend.
Along with economic development, came military fortifications, ports and airfields designed to create offensive bases and a defensive perimeter for the Japanese home islands. Many islands of Nan’Yō become the site of infamous battles in the Pacific war such as Tarawa, Kwajalein, Saipan, Guam, Tinian and Pelieu.
Japan has the sea, but is a small country without many resources. I imagine that this was a fundamental motivation for their invasion of neighboring countries in World War Two. They have since dealt with this problem in other ways, but that’s another story.