War had been an integral part of the life and culture of the Māori people. The Musket Wars dominated the first years of European trade and settlement. The first European settlers in the Bay of Islands formed a volunteer militia from which some New Zealand Army units trace their origins. British forces and Māori fought in various New Zealand Wars starting in 1843, and culminating in the Invasion of the Waikato in the mid-1860s, during which colonial forces were used with great effect. From the 1870s, the numbers of Imperial (British) troops was reduced, leaving settler units to continue the campaign.