World War II: The United States invades Saipan, capital of Japan's South Seas Mandate.

The Battle of Saipan was an amphibious assault launched by the United States against the Empire of Japan during the Pacific campaign of World War II between 15 June and 9 July 1944. The initial invasion triggered the Battle of the Philippine Sea, which effectively destroyed Japanese carrier-based airpower, and the battle resulted in the American capture of the island. Its occupation put the major cities of the Japanese home islands within the range of B-29 bombers, making them vulnerable to strategic bombing by the United States Army Air Forces. It also precipitated the resignation of Hideki Tōjō, the prime minister of Japan.

The South Seas Mandate, officially the Mandate for the German Possessions in the Pacific Ocean Lying North of the Equator, was a League of Nations mandate in the "South Seas" given to the Empire of Japan by the League of Nations following World War I. The mandate consisted of islands in the north Pacific Ocean that had been part of German New Guinea within the German colonial empire until they were occupied by Japan during World War I. Japan governed the islands under the mandate as part of the Japanese colonial empire until World War II, when the United States captured the islands. The islands then became the United Nations-established Trust Territory of the Pacific Islands governed by the United States. The islands are now part of Palau, the Northern Mariana Islands, the Federated States of Micronesia, and the Republic of the Marshall Islands.