the point about the settlement of New Zealand - and it's to Britain's credit - is that it was done via a treaty with the Maori. There were already Europeans there - sealers and whalers and generally scum - and some officials who'd gone out from Britain to try to keep them in order, but without much power to do so. But unlike Australia or America Britain then signed a treaty with the natives before any proper settlements were begun.
There was subsequent fighting, mostly over land rights, and the treaty was widely broken by the settlers. This has been mainly sorted out over the past 20 years or so with big payments to Maori tribes to settle grievances. So I don't think they're still at war - there never was a 'war against Maori'.
Regarding the original question: no idea, because having different species makes it hard to imagine. I think the big question is: can we interbreed? If so then yes, we will gradually merge. The story of the Sabine women more or less illustrates this process, as does the gradual integration of Angles and Saxons and Vikings. It took longer with the Normans because they took over administration of the country and had a different language; but we're all the same people now.
(Ludwig, why don't Americans scratch big cars? Many of them came from Britain too, after all.)