Blockchains are decentralized, but there is a centralized set of rules that all participants must obey. Importantly, this set of rules is (or at least should be) as minimal as possible. These rules are just the code of the blockchain software.
This means the software is basically the constitution of a country. Your citizenship in this country isn't based on where you were born. The immigration process isn't tedious. For most blockchains, you're a citizen if you just own any amount of the native currency.
The minimal constitution of a general purpose blockchain allows anyone to start or join their own states within the federation. Put another way, anyone can create a dApp with its own system of governance. This is your state within the USA. You can be eternal king of your state, hand over full control to your citizens, or dream up a new system.
Most dApps don't plan for states within states, but there's no reason you can't build things this way. If you're designing a game for blockchain, there's fun to be had allowing players to create factions, alliances, gangs, or whatever.
You can do anything with your state, but if you find that the federal government (read: blockchain) isn't permissive enough, you can start your own country.
P.S. Koinos is the first blockchain to allows for tourism.