Why did the Marshall Islands become part of the Trust Territory of the Pacific Islands after World War II?

Following the defeat of Japan in World War II, the Marshall Islands became part of the Trust Territory of the Pacific Islands in 1947 because the United States, having secured the islands during its Pacific campaign, assumed administrative jurisdiction under a United Nations trusteeship.123

Prior to this, the islands had been administered by Japan as a League of Nations mandate following World War I. The transition to a U.S.-administered UN trust territory formalized the American control established during the war, allowing the United States to oversee the region's civil administration until the islands eventually moved toward self-government and sovereignty.123