A Royal Commission
The New Zealand Premier Richard Seddon set up the royal commission in 1900 to buy time and gain an understanding of public opinion about becoming a State of Australia. Richard Seddon himself was not a fan of New Zealand becoming an Australian State. The Royal Commission reported back
that:
The stretch of some twelve hundred miles of sea ... is a weighty argument against New Zealand joining the Commonwealth
But that wasn’t the only argument. New Zealanders just weren’t interested in uniting with Australia. The NZ Ministry of Culture and Heritage
write:
The prevailing view was that New Zealanders were of superior stock to their counterparts across the Tasman.
In Australia, one of the reasons that had been put forward to federate was the need for a united defence force. New Zealanders thought that the British would protect them if
needed:
So long as Britannia ruled the wave, New Zealanders could rely on imperial protection of their own coastline. In the event of Great Britain losing command of the sea, Australia and New Zealand could not rely upon being able to render material assistance to each other.
They also felt as though they were competitors or rivals of the Australia colonies rather than partners. But the Australian colonies also saw themselves as competitors of each other. And New Zealanders also saw no need for a High Court when the Privy Court was available to them.
In any case, the ten man Royal Commission in New Zealand recommended not becoming a State of Australia. But the option was left open for them to join at a later date. Hence why we find New Zealand named in our Constitution where the States are defined.