About that whole
Aang: Prevents Fire Nation from invading Southern Water Tribe
Korra: Leads Fire Nation to invade Southern Water Tribe
the thing is they are actually doing the same thing.
In Aang’s case he persuaded the Earth Kingdom and the Water Tribes (mostly the Earth Kingdom) to attack (or rather counter attack) the Fire Nation becuase the Fire Nation was invading other countries.
Now let’s look at Korra. She may seem to have started a civil war… but come one… how could one person possibly just start a civil war, Avatar or not. It was obvious, even from the first series that the water tribes had a deep unresolved conflict between them and it’s only now that that has shown on the surface.
She is only persuading the Fire Nation to help protect and counter attack the Nothern Tribe because the North invaded the South first. It’s basically the same situation as with Aang.
And if everybody would go back to see the first season of A:TLA, we can see that Aang, Katara, Sokka, everybody also acted immaturely and based on their feelings too. Don’t you remember when Aang hid Hakoda’s message to Katara and Sokka just becuase he thought they would leave him? But they progressed through time and I still believe that these characters will develop as well.