Here's a thought, Unalaq is apart of the Axis powers, Korra and Republic city is apart of the Allies.
Bear with me while I explain the strikingly similar events in Legend of Korra (LoK) and the events in WWII.
Ok, lets do this.
In the beginning of Book 2, Unalaq convinces Korra to open up a portal, and in the process he takes over the southern water tribe claiming that it is to bring back spirituality to the tribe it's self.
This can easily be compared to Hitler taking his rise to power in the name of Germanic purity- or the Aryan race.
Lets fast forward a little bit here; Korra finally discovers that her new mentor Unalaq is actually evil and she rushes to Republic City to ask for help, which they readily deny saying that they do not want to interfere in others affairs.
While Hitler was rising to power, and taking over countries, the Allies had readily denied it happening and were in no condition to fight back, letting the Axis become stronger.
Varrick has decided that he must start using propaganda to force, or convince Republic city to goto war through the use of "Movers" or pretty much just black and white movies. He creates a hero to go up against Hitler (erm, Unalaq) and entice audiences around Republic City to call for arms.
WWII is not just full of travesty, but during this era it is filled with Propaganda on both fronts, many Disney films came out of the war as a way to push towards the war front.
I'm just getting started here but I'm sure you get the idea - do you have any more to point out? What do you think?