And most of this critique of empire is completely lost in Legend of Korra. A show that does nothing to reconcile the past with the present. Instead it preaches literal horseshoe theory as the over arching message of the show.
"what did Amon want? Equality for all. Unalaq? He brought back the spirits. And Zaheer believed in freedom. [...] The problem was, those guys were totally out of balance and they took their ideologies too far. " - Toph, EP 43, "The Calling"
Each of these villains, including the final one, Kuvira, represent a kind of ideological boogie man.
Amon is the minority rights Boogie Man, he espoused the ideals of equality. One could interpret him as the white genocide boogie man but there is little evidence of any kind of true class division between bender's and non-benders. A shallow caricature at best.
Unalaq was the religion or spirituality boogie man, or could be interpreted as the "return to tradition" boogie man.
Zaheer is the anarchist boogie man.
Kuvira is the totalitarian dictator aka Communist boogie man.
At no point in the show does Korra have to struggle against any of these ideas and combat them in any ideological way. They are all metaphorical punching bags. Each of them "to extreme" to allow to exist. Each contrasted against each other as though they were equals.
Republic City stands at the center of the show as the only constant and good political organization. A representative democracy. Tied explicitly to Aang to drive the point home, if you had any doubt's about its goodness. A stand in for America with its own statue of liberty.
In the end, the heir to the Earth Kingdom Monarchy gives up his throne to install a representative democracy in the Earth Kingdom. The result of this shallow attempt at writing leaves the shows saying almost nothing at all. It's as if it was written to tell 13 year olds that their anarchist or communist curiosities are misguided and simply a phase.