Because of the very small number of Europeans who visited New Zealand in the 18th and early 19th century, the core values of Māori culture altered little. Henry Williams estimated there were only 1100 Europeans in the North Island in 1839, with 200 of them missionaries, and a total of about 500–600 Europeans in the Bay of Islands. The northern Māori population at the time has been estimated at about 30,000 to 40,000, down from about 100,000, fifty years before. This drop in population was mostly due to disease and to the Musket Wars of 1807–1837.