Right, thank you all for the context and perspectives.
Just one more thing if nobody minds, is there any serious consideration of the possibility of isolated Uplifted societies? The crab bucket, power balance, politics of the known Ninja Villages caused them to put down known upstarts like the Uzumaki and Samurai but apparently faceless threats that 'just' kill everyone who crosses the border like Rain or Bear don't provoke a coalition against them.
How much densely settled land would you need to out populate the EN? How many generations without warfare to cull the numbers would it take to exceed the chakra-wielding population from a small seed pop?
It kind of seems like the way to 'win' in MfD and get out of the downward spiral. Some of Kagome's village under the sea ideas kind of make sense from that perspective.
The Elemental Nations, if memory serves, are about a fourth the size of Australia (not sure why we used that comparison, but I remember it) in landmass, and we know Fire Country has about 300,000 people in it.
If we estimate about 2,000,000 people in the Elemental Nations total (highball probably, but I'm being generous), then they have a population density of... 1 person per square kilometer, roughly (Australia is 7.7 million km
2, a quarter of it would be just shy of 2 million km
2).
It's estimated
here on Wikipedia that 12th century Japan had a total population of about 7-10 million people. Japan is about 375,000 km
2 by landmass, so that gives us a population density of 19-27 people per square kilometer. I use these numbers because I want to estimate what kind of population density you can achieve in real-world conditions at that tech level, even if it leaves rather wide error bars.
So if you want to match the EN population of 2,000,000 people in a secluded landmass with a population density akin to the IRL equivalent of the Elemental Nations tech-wise, you'd need about 100,000 km
2. To get that, we'd need a 300km by 300 km landmass (or a landmass with 180km radius, whichever approximates better).
By my estimates on the canonical map of the EN, none of the smaller islands reach anywhere near that size. You'd need something like half of the Eastern Continent to house that many people, and you don't stay out of the ninja politics game when you're that size, unless you're really far away (or otherwise inhospitable like Snow, but if you live in Snow you're not hitting feudal Japan pop density in the first place).
The problem is further compounded by having to fend off chakra beasts across your
entire country, which is no easy feat when we're talking scales in the hundreds of kilometers.
Let's suppose you make miraculous feats of chakra-engineering and get your hideaway up to modern Japan pop density (>850 people per square kilometer). Now we're looking at 2,350 km
2, measured as a square ~50km to a side or as a circle ~27km in radius. Something that small could be set up on one or two of the smaller islands on the south end of the map, but remember that we're talking about
modern population density, aka after multiple agricultural revolutions and the industrial revolution and the birth of modern civilization and modern healthcare, which even with chakra-engineering sounds pretty farfetched to me.