The Northern Water Tribe appear European while most of the Southern Water Tribe look Inuit- except for Sokka, Katara and Kanna (their grandmother). In the show, Kanna ran away from the Northern tribe, so perhaps their different ethnicities are meant to reflect that.
That is the official reasoning; they even made an effort to cast mostly Europeans as members of the Norther Water Tribe. It might even confirm a persisting fan theory that Kanna was pregnant with Pakku's son when she ran away, making Sokka and Katara his biological grandchildren. Still...you'd think that the two kids would look just a little more Inuit, considering that Hakoda, at least, married a Southern Water Tribe woman.
The Fire Nation appear to be Indian in this continuity. Considering M. Night Shyalaman's penchant for the Creator Cameo, perhaps he did this to facilitate his future appearance as Uhvatar Roku?
So, Yue's parents died sometime off-screen, right? And now Yue's dead... Who's running the Northern Water Tribe now that the closest thing to a royal family they have is dead?
Mild Adaptation-Induced Fridge Horror: If Aang is the last of the Airbenders and, as the Avatar, is not allowed to have a family, either he has to follow the rules and let Airbending die with himnote Shyamalan knows that Airbending isn't something one can just learn, right? or he says Screw the Rules, I'm Doing What's Right towards his people and marries to continue the Airbender line. Or did Shyamalan envision some Jedi-style Ain't No Rule loophole allowing for attachment-free procreation?
Why would Shyamalan take away the canon Fire Nation's greatest strength (generating their own element to fight with), then replace that advantage with "their machines" THEN show very little of said war machines? He did realize that didn't make the Fire Nation look strong, it made the other nations look weak, right?