The biggest threat to NZ sovereignty is a naval blockade, and such things are still in the book of naval strategies and tactics. The next threat is interruption to our SLOC by nefarious forces, either nation / state or non state actors. Generally speaking NZ pollies and the great hairy unwashed remain ignorant of that threat, which is classic sea blindness, especially for a maritime island nation.
IMO interruption of the SLOC is a greater threat, in part because it is so much easier to accomplish. OTOH though, what I consider an 'interruption' others might consider a blockade or part of a blockade.
While you are correct as to the current situation this can change far faster than we can rearm. We must also not forget the emergence of rogue organisations who do things that defy logic and they have away of quickly subjugating a population. Who is going to resist them if they know their whole family will be executed if they try.When we look back on past conflicts we see that a lot did not have a lot of logic involved and that the resisting population was a very small part of a percent of the population which took a significant period of time to build and often had to rely on extensive outside help to achieve significant results. As a worst case scenario we could be subjected to ethnic cleansing. the point being we don't know what the future will bring and my thoughts are that we should project sufficient deterrent to ensure that no rogue nation or organisation tries any half baked ideas in our direction. The simple truth is that we are ignorant as to the future and we tend to project our minds into the future on the basis of what is happening now and how that will play out. It is one of history's quirks that there are sudden changes in direction. Who would have foreseen the rapid rise of ISIS say 10 years prior to their advances, or say the Falklands war in say 1973 or for that mater most conflicts. No one did. Our strategic situation will change with time sometimes for the better and sometimes for the worse and that is what we need to be prepared for. We just need to remember that just because we cannot see any possible way that we may be threatened does not mean that someone else cannot come up with something we did not think of. The limits of anyone particular person's mind is not the limits of someone else intent on usurping them in some way or other.
I agree that future threats will likely emerge faster than then NZDF can, or would be funded/permitted to re-arm sufficiently to meet.
At the same time though certain realities exist with NZ's defence situation, which very often seem to get ignored by both those advocating for significantly greater and lesser defence spends.
Those advocating for less defence spending tend look at how remote NZ is, rightfully conclude that an invasion and conquest as a practical is virtually impossible and decide to argue that the NZDF does not need to be as capable as it is because anything short of an invasion and conquest does not constitute a threat.
OTOH there are some among those advocating for greater funding and support for the NZDF who seem to only consider how little the NZDF can do against direct, existential threats to NZ proper and focus on building capabilities to combat these direct threats, all while ignoring the difficulties an aggressor would face if they attempted to exploit gaps in NZDF capability to carry out a direct attack.
Both sides always seem to focus so much just on threats within NZ home waters or NZ soil while ignoring the impact on NZ of threats and events further away. I am uncertain if this is because of 'sea blindness' as some have described it, or because the threats and events might not even be intended to impact NZ
What I have been advocating for is the NZDF to at least maintain, if not expand it's capabilities to cover a broad range of potential threat scenarios, particularly focusing on those threats which can be most easily realized and have a significant impact on Kiwi life.
In terms of the likelihood of a direct, existential threat to NZ, let us change some of the numbers around and re-examine it, shall we?
Instead of assuming that 1% of the NZ population would be willing to take up arms, how about we assume 0.1% instead. That would be ~4,200 per the 2013 census, which is actually about 500 less than the number of regular NZ Army personnel. Keeping the ratio of 7-10 troops per resistance or guerrilla fighter, an occupying army would need "only" 29k - 42k troops. Even with the size of the hypothetical army of occupation being a tenth of what it was before, just how many nations have an expeditionary force that large? How many nations have sufficient logistical assets to maintain an air and sea bridge large enough to support and sustain a force that large and that remote?
From the above numbers, we are looking at a force that is as large or larger than the entirety of the Australian Army. In fact, less than half of the world's nations maintain standing militaries (army, navy & air forces combined) with the total personnel numbering over 29k. The number of potential occupiers drops further when one considers that any such occupier would need to retain sufficient personnel in their home country to meet their self-defence needs. Assuming that 75% of a nation's military was needed to maintain self-defence, and that the occupation force only needed ~30k personnel, less than a quarter of the world's nations maintain large enough standing forces. Then these would-be occupiers need to have enough air and sea transports to maintain the flow of food, fuel, parts and replacement personnel. Of the nations with large enough militaries, Indonesia is the closest to NZ, at ~5,000 km, and the next closest would be Thailand, at just under 10,000 km away.
When examining the potential threats to an invasion of NZ, there are just not very many nations that have the resources to accomplish it. In point of fact, I suspect only a single nation could do this at present or in the short/medium term future. I suspect NZ has a greater chance of being impacted by a major earthquake of eruption before another invasion.
