Alright this one is hard, and I understand why it exists.

War is an instrumental part of any fantasy novel.
It's a given and I whole heartedly approve.
However, I've found that written wars are very small minded and very one sided.
One side is all purity and goodness, and is the only way, and the other is the big bad, and while there may be good people on that side, ultimately they end up switching over because there couldn't possibly let be any merit about the "evil" side of the war.
To be fair, it's always easy and it's always entertaining to write a one sided war.
Everyone wants there to be little emotional baggage and conflict when it comes to choosing sides. 
HOWEVER.
"Battles are ugly affairs."
(I'm sorry I had to.  Narnia reference.)
Anyway.
I didn't really think of the duality of war and conflict until a few years back, when I really analyzed some well written movies and books.
Kingdom of Heaven.
It shows the battle for Jerusalem between Saladin and Baldwin IV, the Muslims and the Christians, just before King Richard's crusades.
We watch from the perspective of Christians, and yet this Christian king goes to his death to ensure peace between Christian Jerusalem and the ever present Saladin, who is labeled outright as a man of respect and honor. 
There is corruption on both sides, and yet both sides have undeniable merit. 
The mutual respect, and the conflict of history really draws on the fact that this was truly an accurate representation of what war is like.  It's bad, and bloody, and hard to deal with, because you know that the man in front of you is fighting for his honor, his people, and most likely the same version of family you have at home.
The movie Troy (obviously the Iliad, but anyway)  also depicts this very well.  Both the Trojans and the Greeks, despite the undesirable Greek king and the conquering force that they became, were respectable people.  Hector's death at the hands of the great Achilles ends with great suffering and regret on both ends. 
There are endless, ENDLESS examples of the duality of war and why it is never black and white, good and evil. 
This is getting pretty long now, which is why I'll cut the rest out, but I hope this has cut down the expectation that war must always be the knight on his white horse against the evil dark lord and his mindless minions. 

Honorable mentions that I would love to discuss in further detail concerning double edged wars