He didn't have an easy time of it. After many years of fighting and peace-making, the only lands he could control were a few districts on the Big Island and, through a diplomatic marriage, another few districts in Maui.
The breakthrough came when he turned to foreign traders. Admittedly, foreign ships had been visiting the Hawaiian islands for quite some time. Its location in the middle of the Pacific made it a useful halfway point in many journeys. Whenever possible, Kamehameha traded island goods for weapons.
After several victories, he was eventually drawn into another stalemate as other powers began amassing their own stock of Western weapons. It wasn't until a timely volcanic eruption all but wiped out the army of a rival leader that Kamehameha turned things around again. He then invited his rival to a peace meeting to discuss their differences. Upon landing, the rival was swiftly executed and offered as a sacrifice to the god of war. And with that sacrifice, Kamehameha became the undisputed ruler of the big island, Hawaii.
Maui, the next island on Kamehameha's wishlist, was exhausted after a war against neighbouring Oahu and soon fell to Kamehameha's forces.
The ruler of Oahu knew what was coming and beefed up his arsenal of American weapons. However, even that was no match for Kamehameha's tactics and he eventually fell.
Kamehameha next wanted to take Kauai, but rebellions in his holding forced him to bide his time. A few years later, Kauai was struck with an outbreak of cholera. Seeing his weak position, the ruler of Kauai agreed to become Kamehameha's vassal, a bitter arrangement that the ex-ruler resented. Nevertheless, Kamehameha finally held all of the populated Hawaiian islands.
After conquering all of the islands, Kamehameha set upon boosting the government, economy, and foreign relations. He actively encouraged trade of the islands' resources and quickly grasped the concept of currency. Trade flourished, especially with America, Britain, and eventually Russia. He maintained a group of trusted advisers and administrators, and took steps to ensure they guided his son and heir after his death.
Upon his death, Kamehameha was buried in a secret grave to ensure his bones would never be disturbed. He was succeeded by his son, crowned Kamehameha II, and his wife, now queen regent. These two ushered in a series of reforms that changed Hawaii for ages to come.
Sources:
"Captive Paradise" - James L. Haley
