Are you sure that WWII isn't TWO examples?
Had you asked any Nazi before the invasion of France, he likely would have said that Germany's actions to that point were largely a matter of Germany "rescuing" its fellow Germans from their (Jewish-led) oppressors in Poland and Czechoslovakia. His arguments would probably not convince you, but they would be sincere and not trivial to refute.
I don't mean to sound facetious, nor to denigrate the heroism of the allies in that war. I mean only to illustrate that few events are so easily classified as a "rescue". It is rare that doing the "right" thing doesn't also serve self-interest in some way. And conversely, few wars are started without some justification that can be called "righteous".
Thus we have historians - people who enjoy teasing out the threads of truth in these knotted narratives. We routinely see the villains of one generation being rehabilitated by subsequent historians as time gives new perspectives and research provides new data. And even more often we see heroes brought down to the level of their enemies - indeed, something about our modern culture makes this process trivially simple nowadays.
Thus, I encourage anyone who is interested in history to make a point of reading (or watching) not just the latest books and videos, but works from early eras. In doing so you'll learn much more about the period you are studying - and also the period you are living in!