While the way 1700s British acted would not meet modern British standards, it's a hell of a lot closer to them than Maori behavior and values of the same time period. In the mid-1800s some Maori invaded the Chatham Islands and enslaved, killed, raped, and ate the population (called the Moriori). Here's a quote from Wikipedia:
A Moriori survivor recalled : "[The Māori] commenced to kill us like sheep.... [We] were terrified, fled to the bush, concealed ourselves in holes underground, and in any place to escape our enemies. It was of no avail; we were discovered and killed – men, women and children indiscriminately." A Māori conqueror explained, "We took possession... in accordance with our customs and we caught all the people. Not one escaped....."[38] The invaders ritually killed some 10% of the population, a ritual that included staking out women and children on the beach and leaving them to die in great pain over several days.[34]
If you're interested in learning more you could read some ethnographies of modern-day (or close to modern day) primitive peoples. The Yanomamö work thinks a lot about violence because people (the antrhopology community) couldn't even believe how violent they are. The other way to go about it is to think about the development of morality in humans (like moral universals). One theory goes small gods who are fallible and many --> big gods who always watch and are few --> the kind of normative morality software you have installed right now, which doesn't depend on gods.