This is something rather intriguing that I noticed when I was rewatching the 1st season of the original Avatar series regarding how different nations tend to act towards citizens of either their own nation or others in certain situations, and it goes to show how creative the creators are in showing that not everyone is like how you would think that they's act like.
The two episodes I'd like to discuss are "Imprisoned" and "Jet". Recap of what happened in the beginning of "Imprisoned": Aang, Sokka, and Katarra come upon Haru practicing his earthbending, who then promptly runs away once he knows that the gang is watching him, fearful that they would turn him in to the Fire Nation soldiers who are running his village because Earthbending has been made "illegal", in a sense. Later on, the gang and Haru try to help an old man from Haru's village, who has become halfway trapped in a collapsed mine. Through the use of Earthbending, Haru manages to save the old man from certain injury/death; but instead of being grateful for having his life saved, the old man turns against Haru and rats him out to the Fire Nation soldiers.
A stark contrast to this particular scenario is found within the episode "Jet". As we all know, Jet let his anger and hatred towards the Fire Nation overtake him and make him go crazy with wanting to get revenge towards them for ruining his life and those of others, wanting to go so far as to wipe out an entire Earth Kingdom village full of innocent people. Remember when Sokka went with Jet and a few others to do some spying/stealing from Fire Nation soldiers/citizens for supplies? Sokka tried to stand up for an elderly Fire Nation citizen after seeing Jet and his gang bully the poor man for no good reason other than the fact that...they just could. Well, it paid off for Sokka to stand up for the old man, as it was only the old man who believed Sokka when Sokka tried to warn the villagers of Jet's dastardly plan.
What I'm basically trying to get at here is that not everyone from each nation acts how you would think that they would, considering where they're from. Regardless of whether you've saved someone's life or you stood up to their bullies, whatever, depending on what the situation is about and circumstances leading up to or after an incident, can help to determine why people act the way that they do.