Generally, only female slaves were kept as they were considered to be less of a threat and more useful as potato farmers and partners. In 1834 Ngapuhi, partly due to the influence of missionaries such as Henry Williams, freed slaves they had captured in earlier wars, The only place in New Zealand where slavery was common after 1835 was in the Chatham Islands. During the Musket Wars, North Taranaki tribes Ngati Tama and Ngati Mutanga invaded, massacred and enslaved the remaining population until about 1863.