Complex sentence: Captain Sumner, from Northampton, was an early settler of Hawaii who arrived in 1807 as a cabin boy; initially befriending Kauai's king Kaumualii, he later became a naval captain under King Kamehameha I, who united the Hawaiian Islands in 1810.
Split into simpler sentences: Captain Sumner, from Northampton, was an early settler of Hawaii who arrived in 1807 as a cabin boy. Befriended by Kauai's king Kaumualii, Sumner late advanced to the rank of a naval captain under King Kamehameha I, who united the Hawaiian Islands in 1810.