Re: Why did the League of Shadows want to destroy a peaceful city?
Well the way I see it is that Nolan couldnt throw the whole Bane/los history and timeline(from the comics) in one movie.
In the comics, Bane starts off as a mercernary, breaks the Bat, gets his ass kicked by that blonde dude taking steroids, then after a while - as RAG suggests to Bruce in Batman Begins - becomes truly lost; he is looking for a cause and joins the LOS (and in the process falls in love with Talia).
There is also one comics where Bane fights Batman again, and Bane tells him during the fight that he wants to take the LOS over; to which Batman replies : " lol there is no ****ing way RAG is gonna let that happen " (or something like that)
Sure in Nolanverse he is trained by RAG and then gets kicked out by the LOS, but other than that...
Plus, he was referred to as a "mercenary" early in the movie