In accord with Plato I consider the purpose of the state to be to benefit its people.
I would be surprised to find any individual in the world who would say they are 100% satisfied with the nation state they live in. I am amongst the many who are dissatisfied with the nation state of Britain, for regardless of what set of politicians are elected they never seem to be able to serve the interests of Britain but themselves.
Some of the finest works of philosophy have been produced because of thinkers who tried to find a solution to the failings of the nation state of the day. Plato produced numerous works in the light of the constant crisis in Athens. Confucius produced his work to answer his despair at failings in China. Then there is Thomas Hobbes and his great work Leviathan in the aftermath of the English Civil War between King and Parliament. In my opinion none of these philosophers have been able to find the right solution to the issue of the perfect nation state.
I consider like Plato that the State exists for the benefit of its people, and thus should take no action that works against that aim. Secondly, I think many of the problems of the state is down to size, that the peoples are too many, too diverse and spread over too wide an area to be all satisfied by a single system. My answer to this is the Greek idea of a Polis, a city state that is neither too large or too small. My town of Colchester would make a perfect city state, with the town, plus six miles of farmland around it, and a few villages making a self supporting city state.