The ancestors of Native Hawaiians may have arrived in the Hawaiian Islands around 350CE, from other areas of Polynesia. By the time Captain Cook arrived, Hawaii had a well-established culture with a population estimated to be between 400,000 and 900,000 people. Starting in 1795 and completed by 1810, Kamehameha I conquered the entire archipelago and formed the unified Kingdom of Hawaii. In the first one hundred years of contact with Western civilization, due to disease and war, the Hawaiian population dropped by ninety percent, to only 53,900 people in 1876. American missionaries would arrive in 1820 and assume great power and influence. Despite formal recognition of the Kingdom of Hawaii by the United States and other world powers, the kingdom was overthrown beginning January 17, 1893, with a coup d'état orchestrated by, mostly, Americans within the kingdom's legislature, with aid from the United States military.