Oahu (pronounced /oʊˈɑːhuː/ in English) or Oʻahu (pronounced [oˈʔɐhu] in Hawaiian), known as "The Gathering Place", is the third largest of the Hawaiian Islands and most populous of the islands in the State of Hawaiʻi. The state capital Honolulu is located on the southeast coast. Including small close-in offshore islands such as Ford Island and the islands in Kaneohe Bay and off the eastern coast, it has a total land area of 596.7 square miles (1,545.4 km2), making it the 20th largest island in the United States. It is also the most populous island in the Western Hemisphere that neither contains a national capital nor possesses a road or rail connection to a national capital. In greatest dimension, this volcanic island is 44 miles (71 km) long and 30 miles (48 km) across. The length of the shoreline is 227 miles (365 km). The island is the result of two separate shield volcanoes: Waiʻanae and Koʻolau, with a broad "valley" or saddle (the central Oʻahu Plain) between them. The highest point is Mt. Ka'ala in the Waiʻanae Range, rising to 4,003 feet (1,220 m) above sea level.

The old Kingdom of Oʻahu was once ruled by the most ancient Aliʻi in all of the Hawaiian Islands. The first great king of Oʻahu was Mailikukahi, the law maker, who was followed by many generation of monarchs. Kualii was the first of the warlike kings and so were his sons. In 1773, the throne fell upon Kahahana, the son of Elani of Ewa. In 1783 Kahekili II, King of Maui, conquered Oʻahu and deposed the reigning family and then made his son Kalanikupule king of Oʻahu. Kamehameha the Great would conquer Kalanikupule's force in the Battle of Nuʻuanu. Kamehameha founded the Kingdom of Hawaiʻi with the conquest of Oʻahu in 1795. Hawaiʻi would not be unified until the islands of Kauaʻi and Niʻihau surrendered under King Kaumualii in 1810. Kamehameha III moved his capital from Lāhainā, on Maui to Honolulu, Oʻahu in 1845. ʻIolani Palace, built later by other members of the royal family, is still standing, and is the only royal palace on American soil.



