Nation sizes between 1 million - 100 million ?
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 Obviously these are arbitrary guesses on what might work, mostly
 having current European culture in mind.

 The system isn't a "closed" system in the sense that if the
 population where to drop dramatically, as long as you have
 at least 50 * 50 persons for one council, then maybe there
 might be too few people and therefore too few nations each
 nation having unneccesary amounts of land.

 So maybe this rule will do:

 - The more honorable a people are, the smaller a nation they
   can have. For example one could say that for every 100
   years there is not a war in/by a nation, the minimum amount
   needed to start a nation is cut in half.

 - One could also make it some sort of 'rule:' there are always
   at least, say, 50 possible nations on Earth (using 50 again).
   The population number varies (including times of war) between 
   total population of Earth / 50 to 100 times smaller (roughly).
   That would mean: 6,500,000,000 people now, puts the upper
   margin for a nation at 130 million (which in my opinion
   is far too large, but okay). You could also use the 100
   million marker at the present and say there should always be
   at least 65 nations, the largest then possible at 100 million
   (which in my opinion is also far too large, but it's not that
   great to have a strict rule near the optimum - should allow
   for experiments with 'too big' too, see how that goes and
   to satisfy that want within the framework).

   The corresponding minimum sizes would be 1.3 million and
   1 million respectively, depending on present day world
   population.

Suppose morality and so on on earth would one day peak at high
levels, people could even become capable of having extremely
small nation sizes, even nations of 1 person.

We could also say something like: those nations who have not
launched offensive wars outside their territories, from that
day the clock starts ticking on how small nation they could
be allowed to break away with. Hence a nation that hasn't
launched a war beyond its established borders for 5 centuries,
they would then have a moral but practically computable
claim to break away with 1,000,000 / ( 2(1) * 2(2) * 2(3) *
2(4) * 2(5). 1,000,000 / (2*2*2*2*2) = 31,250 persons
(thirty one thousands and a quarter thousand).

It's always good and well to make moral claims, it's a lot
more useful if they can be turned into practical results
and functioning protocols.

This scheme could be used as some sort of contribution to
a debate about breaking away. If you'd want to put some of
it into law, you obviously need to adapt the given Constitution.
That said, the Constitution as proposed isn't functioning before
it is functioning, isn't it; nations can also be formed outside
Constitutional protocol, for example in nations that haven't
enacted this Constitution (or are in such an unfinished process).

*

Instead of "no war" you could also use "no murder inside the
nation," which might be better (considdering that a murder
is a person to person war.)