The Kingdom of O'ahu is the smallest of the four kingdoms of the United Kingdoms of the Fuximi Islands in area, and largest in population. O'ahu has had a history of being in personal union with one of its neighbors. In 1819, King Kalanikupule of claimed the throne of Maui after the later broke away from Hawai'i. Upon his death in 1821, leaving no heirs, King Kaumu-alii I of Taua'i claimed the throne of O'ahu, initiating a personal union of three of the four Fuximian kingdoms which lasted until 1849, when King Keali'iahonui died without heir, and all three kingdoms elected a new king.