Most popular answer on this question is Switzerland???
New Zealand would be the safest country and Australia, a very close second.
You want to think about strategy? logistics ALWAYS comes first!
As well defended as Switzerland is, the oldest form of taking a defensive structure would inevitably destroy them.
Siege
Switzerland is almost entirely dependant on imports for their food. There simply isn’t enough fertile ground to support their population of 8.3 million.
You want to beat Switzerland? Starve them.
They can hide behind their broken bridge, rock covered mountain roads, fallout shelters and armed forces all they like. But without food Switzerland is screwed.
It wouldn’t take more than a few months before Switzerland is forced to surrender.

Australia has a massive natural advantage.
Australia is surrounded by water. Australia also has no nearby foreign deep sea ports capable of staging an amphibious assault. This means that any amphibious task force would require massive supply chains which would be very difficult to maintain and defend.
[1]

Australia has has a small but highly motivated and experienced defense force of 58,000 personnel.
But these guys are who you really need to worry about. These bastards are unbeatable.

‘The Great’ Emu War – Wikipedia
If the attackers make it to Australia, well guess what… you have probably just reached northern Queensland or Darwin. That’s all the way in woop woop (middle of bum f**k nowhere).
The next closest major urban center would be Brisbane and that’s 3,424km from Darwin.
Also guess where Australia keeps an decent chunk of their defense force?
Darwin. *wink wink*
[2]

[3]

You want to lay siege to Australia?
You are on the right path. But unfortunately for you “our land abounds with nature’s gifts”. Australia has abundant fertile land to farm. More than enough to be self sufficient.
As for Nukes. Yeah piss off, we are so big that if you wanted to destroy all of Australia then you would throw enough fallout into the atmosphere you would inevitably doom earth. We all die in that scenario.
In essence, to achieve a successful landing on mainland Australia would be a logistical nightmare. To capture anything important would require a miracle.
New Zealand is shares very similar characteristics as Australia but NZ is even further away from everything else. NZ has a disadvantage due to their smaller size but their distance factor makes up for this.
Australia and New Zealand have enjoyed a very strong relationship since their creation and getting to New Zealand would mean facing the wrath of the entire Australian Defense Force as well.
Also many people outside of the Commonwealth don’t even know New Zealand exists. New Zealand is the most low key country there is. And good relations with pretty much everyone helps NZ quite a bit.
The New Zealand government already understands their defensive position, which is why they have an extremely small defense force of 11,440 personnel but their measure is similar to that of Australia’s defense force personnel.
Finally to emphasize the effectiveness of the ANZAC
[4] forces I’ll leave this quote [5].
“If I had to take hell, I would use the Australians to take it and the New Zealanders to hold it.” -Erwin Rommel.
So to all potential attackers of WWIII, you want hell? Come take it!
[5]. Historical accuracy of this quote is debatable. Even if it’s false the adf has been coined the best small army in the world on many occasions.
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The US Army’s Forgotten Food Miracle And 126 Superfoods That You Can Store Without Refrigeration for Years
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