I found Iperios and it is a modded server where you can make your own nation. You get to decide your government style and set laws and ranks. If you do not want to make one you can join a nation that already exists.
It runs on All the Mods 10 ATM10 version 6.1. You have to get whitelisted through their Discord first. After you get in a staff member helps you and gives you a beginner kit so you can start playing.
I found a growing nation called Rio de La Plata on a server named DiplomaticaMC. It is an earth style server where people care about politics and government and it feels like joining a real country in Minecraft.
You can become a citizen in a town and build up your own business stuff. If you want more power you can become a mayor and get funding to help your town start growing.
If you like politics you can run for office or start a political movement. The server also has a unique war system and it is crossplay. People say the community is very friendly.
I found this modded server called Iperios and it is all about building nations inside Allthemods 10 version 5.4. You can make your own nation and pick your own government style and set laws and ranks or you can just join a nation that already exists.
To get in you have to join their discord first and ask to be whitelisted. After that there is a channel for new players where you can read starter info and get the server ip.
When you finally join the server a staff member helps you out. They guide you a bit at the start and give you a beginner kit so you are not lost and then you can go off and start playing.
You need the ATM10 modpack on version 5.4 installed or it will not work so make sure to set that up before you try to join.