Based on the movie alone, the origin of Scar's hatred of his brother, and the exile of the hyenas are both unknown.
It is implied that the hyenas are slobbering mangy stupid poachers, and that Scar is simply evil. But those are assumptions; we don't really know what happened.
The hyenas weren't evil, they were only following Scar's orders because they were hungry. But, you have to ask yourself, why were they hungry? Why wouldn't Mufasa let them live in the Pridelands, where there was food? Until those questions are answered, we really can't judge Mufasa's actions as king.
As for Scar, it is entirely plausible that he had a reason to be jealous of his brother. Perhaps if Mufasa had given Scar a role in the kingdom, instead of treating him like useless garbage, things might have been different. I, for one, can totally imagine a young Mufasa spitting in his brother's face and saying "Na-na-nah-nah, you're not going to be king!"

Just his name itself carries a heavy emotional weight.
Scar.
Think about that.
Heck, he was basically at the very bottom of the pride's social pyramid. Even a talkative bird had a greater status in the kingdom. The sad thing is, it certainly wasn't because he couldn't have been a helpful asset. We know what Scar is capable of; he was quite brilliant, and very cunning.
I can only help but wonder if Mufasa had even given him a chance, to put his abilities to a use that would have benefited their society. I get it - Scar was narcissistic and wanted power and all; but the truth is, the only people who want power are the ones who don't have it. Scar was nearly powerless, and not necessarily rightfully so.
In the end, Scar's demise was his own fault, and I do believe that his hatred got the best of him. But, at the same time, I really find it difficult to imagine that Mufasa wasn't at fault as well.
His name is Scar. He was obviously mentally scarred. Judging by the way Scar acted when he was king, the catalyst for that scar was Mufasa.
Scar: I'm ten times the king Mufasa was!
Scar: You know the law: never, ever mention that name in my presence. I am the king!
That's the scar, right there. That is where Mufasa failed. I am not going to question that he was a better king than Scar, but Mufasa definitely failed as a brother.
I certainly don't have any sort of vendetta against Mufasa or anything, but if there's anything I know for sure, it's that no one is perfect. I don't even think Mufasa knew what he had done to his brother until it was too late.
Ultimately, I think that is the significance of Simba's Pride. Mufasa was never perfect, like he was portrayed to be in the first movie. As a result of the entire ordeal with Kovu and Kiara and the Outlanders, Simba realized that - and corrected it in the end.
My conclusion: while Simba made plenty of mistakes as well, when he realized his father wasn't perfect, he became the better king, hands down.
Simba: I was seeking counsel from the Great Kings.
Nala: Did they help?
Simba: Silent as stars. My father would never-
Nala: Oh, Simba... you want so much to walk the path expected of you. Perhaps Kovu does not.
Simba: What? How do you know what-
Nala: I can see them down there just as easily as you can. Get to know them and see.
My other conclusion: Nala should be replacing Mufasa.






