War changed the face of New Zealand in the 19th century. Tens of thousands of Māori died in the intertribal Musket Wars between the 1810s and the 1830s. Muskets revolutionised intertribal warfare, decimating some tribes and drastically shifting the boundaries of areas controlled by others. Thousands fled their traditional lands, complicating questions of ownership and opening large areas to potential Pākehā (European) settlement.
Between the 1840s and the 1870s British/colonial forces fought Māori to open up the interior of the North Island for settlement in conflicts that became known collectively as the New Zealand Wars. Sovereignty was contested on the ground despite the signing of the Treaty of Waitangi in 1840, and Māori became less willing to sell land to the rapidly growing European population.
Many Māori died defending their land; many other Māori allied themselves to the Crown primarily to ensure hapu survival, protect whakapapa, and to affirm mana whenua ownership of their tribal estates. Of the several thousand people killed during the New Zealand Wars most were Māori, and the land of many of the survivors was subsequently confiscated. https://nzhistory.govt.nz/war/new-zealands-19th-century-wars/introduction