This nations idea sounds good. Maybe when people log onto the server it randomly places them in a nation. They can't leave and join another to stop the griefing. Maybe have 3 weeks of building/ gathering and 1 week of raiding the other nations. Possibly having a nation in each of the biomes (sand, forest, snow etc). If it's going to be nations and certain people are going to "lead" maybe have some sort of election system incase a leader is inactive, a bad leader or just plain ignoring people.