Also, at the end of every season, the political state changes. While the world rejects the extreme new systems, it incorporates positive aspects of each.
Communism wouldn’t work, but the world needs equality for all. So, the appointed council is disbanded in favor of a democratically elected president.
Theocracy wouldn’t work, but the world can’t abandon spirituality (which is a fact in this universe, everyone knows spirits exist). So, Korra leaves open the spirit gates so that everyone can coexist with the spirits rather than be ruled by them.
Anarchy wouldn’t work, but the state of the world necessitated agents that could work outside the laws of established governments. So, Tenzin has the Air Nomads working as an international peacekeeping organization (which is its own nation).
Fascism won’t work because it gives too much power to one person (Kuriva) and crushes individuality for the sake of the state above all else. Makes you wonder how the world of Avatar will change next.