Firstly, this assumes large biomes. Biomes will serve as the fundamental unit of territory (this may exclude rivers and extreme hills edge biomes, or very thin mountains adjacent to a biome, or especially small biomes located amidst or adjacent to another biome)

A nation would be restricted to claiming 1 (2, or 3, depending on how people feel about it) biomes.

A nation must be formed bordering another nation (alternatively, within 1 or 2 biomes of another nation).

Oceans count as a border between nations, so a nation may claim land across the ocean from another nation. Sea borders will remain fluid. Archipelago/minor island nations would need to be worked out.

The only way a nation may expand its territory is through conquest of another nations territory (as an alternative rule, a nation my claim 1 biome for every 5 ACTIVE players AT THE TIME OF THE CLAIM). A nation may be conquered biome-by-biome.

A nation which has conquered another nation's territory may do with it as they please (alternatively, it could be said that a national settlement may not be altered without the representative of the nation's permission, though it would belong to the conquering nation)

Independent non-political settlements would retain all rights to autonomy, a nation may not interfere with an independent non-political settlement (and perhaps its buffer territory, which could be restricted to a certain number of blocks around the settlement or scale with settlement size). An independent non-political settlement is associated with the land it is built on.

However, the land on which a non-political independent settlement would in name belong to the nation which has claimed it. This does not mean in any way a nation may interfere with the settlement or its buffer area, but in disputes among nations the land is to be said to belong to the nation which claims it (it may be included on maps of their territory). The settlement may choose what relations it has to the nation which claims its territory (considering itself as a free city, associating in roleplay as a member city of the nation, or completely ignoring the nation and going on as it pleases). If a biome is conquered by another nation, the land on which the settlement is built changes hand, though the settlement retains all rights it had previously and may again choose how it will associate with the political nation.

Furthermore, we can additionally require that a nation must ask a pre-existing settlement before it may claim the biome it is built in. If refused, the biome itself is omitted from the claims rules and nations may claim biomes neighboring the biome which the settlement is built in. A non-politcal settlement may also be built in a nations territory, though they must first make a request to the nation which owns the territory.

Citizens of independent non-political settlements may not count towards a nations citizen limit. An independent settlement may not be founded by a citizen of a nation (To prevent nations from building an independent settlement in order to hop borders or claim a biome they cannot support with their current population). A player may not be a citizen of more than one entity (nation or independent settlement). If ALL of an independent settlements citizens become citizens of a nation, then the biome reverts to unclaimed status and may be claimed by a nation (this is to prevent nations from using independent settlements in order to hop territory, if the settlement has one inactive non-political citizen then it may not be claimed).

The size of large biomes (16x times the size of a normal biome, or 4x larger in each direction) should be able to accomodate multiple settlements

At the beginning of the map, an appropriate location should be found to accomodate nations. Seeds should be explored for a good mix of terrain to facilitate this ruleset).