[citation needed] On January 19, 1778, Oʻahu was the first of the Hawaiian Islands to be sighted by Captain James Cook during his third voyage of discovery.

The next year, on February 27, 1779, Cook's second in command, Captain Charles Clerke, became the first recorded non-Polynesian to visit Oʻahu when he landed at Waimea Bay.

Earlier that month, Cook had been killed at Kealakekua Bay on the island of Hawaii when a dispute with the local people turned violent.

[11] Clerke's visit to Oʻahu was brief and the expedition's two ships left Waimea Bay the same day after finding it difficult to obtain fresh water.

[14] In January, 1893, a group of leading American businessmen took up arms near ʻIolani Palace and, along with US Marines from the USS Boston that landed in Honolulu harbor, launched a successful coup d'état against Queen Liliʻuokalani.

[15] On the morning of December 7, 1941, the Imperial Japanese Navy launched a surprise attack on Pearl Harbor, Oʻahu, bringing the United States into World War II.

[16][17] After World War II, Oʻahu became a tourism and shopping destination with more than five million visitors per year, mainly from the contiguous United States and Japan.

[18] Like all other Hawaiian Islands, Oʻahu was formed from the volcanism associated with the Hawaii hotspot; it started to grow from the sea floor 4 million years ago.

[19] Today, the island is composed of the remnants of two extinct and extensively eroded shield volcanoes: the Waiʻanae and Koʻolau Ranges, with a broad valley or saddle between them.