The Maori were Polynesian navigators who were the first humans to settle NZ around 1300 AD. New Zealand and Hawaii were two of the last places on Earth to be settled by humans.
Then some of the Maori left from NZ and colonized the Chatham Islands around 1500. Due to their geographic isolation, they diverged culturally from the Maori, adopted a pacifist way of life, and came to be known as the Moriori.
In the mid-1800s, some Maori tribes, armed with muskets obtained from trade with Europeans, invaded the Chatham Islands and committed a genocide for nearly 30 years against the Moriori, who did not fight back because of their belief in pacifism. This is known as the Moriori genocide.