It is my understanding that NZ was settled as a colony along the same time as New South Wales and as a result , many of the settlers/convicts would feel inherently British with a shared national identity. What events happened between 1788 and 1901 happen for New zealanders to choose not to opt in a federationand form their own national identity? Furthermore, if NZ always had an option to opt in after 1901, were there any significant movements to rejoin Australia? And if so, Why did they fail?
There's always more that can be said, but you might enjoy starting with this answer from /u/funkyedwardgibbon.