SARUMAN: The world is changing. Who now has the strength to stand against the armies of Isengard and Mordor? To stand against the might of Sauron and Saruman, and the union of the two towers? Together, my Lord Sauron, we shall rule this Middle-earth.
At the base of the war is the desire for power, for control, for total dominance of an entire continent. There are few political intricacies, this is simply Saruman and Sauron's war of aggression, to take Middle-earth for their own.
As Aragorn, Gimli, and Legolas come to the pile of smoldering orc bodies, the camera first gives us a close up on an orc head skewered on a pike.
We know that the orcs are savage beasts, but this is a little taste of the violence of men. The focus on the head shows the Rohirrim's intent to display their brutal handiwork, and we realize that just because they're "good guys" doesn't mean they're asking for surrender and taking prisoners.
GANDALF: Through fire and water, from the lowest dungeon to the highest peak, I fought with the Balrog of Morgoth. Until at last I threw down my enemy and smote his ruin upon the mountainside.
Gandalf's ascension from Gray Wizard to White Wizard isn't accomplished through good deeds or passing the Wizard test; this isn't Harry Potter. Gandalf must fight and defeat a Balrog, his journey through this test commensurate to his journey through Middle-earth; it is one of violence and war. Even the traditions of Wizards are steeped in warfare, which makes sense as this history of Middle-earth is about with conflict.
THÉODEN: I know what it is you want of me, but I will not bring further death to my people. I will not risk open war.
ARAGORN: Open war is upon you, whether you would risk it or not.
War is not a choice in Middle-earth; it is a means of survival. Théoden thinks he can save his people by retreating, but Aragorn and Gandalf want him to face the enemy head on. Neither seems like a great idea, but a choice must be made.
TREEBEARD: War? Yes, it affects us all: tree, root, and twig.
No one is left unaffected by the great war that Saruman and Sauron are waging. Treebeard understands this, we just hope that the nations of men and elves can get their act together and start helping each other fight the enemy.
THÉODEN: Yes, yes, the horn of Helm Hammerhand shall sound in the Deep one last time. Let this be the hour when we draw swords together. Fell deeds, awake. Now for wrath, now for ruin, and a red dawn. Forth Eorlingas!
Impassioned by Aragorn's plea for a final charge, Théoden issues this war cry as he charges out into the battle for a final push, sure that he is going to his death. And these words shouldn't be taken lightly: wrath, ruin, and red dawn? These are violent words. Théoden isn't shouting "for the defense of the women and children." He pumps the blood of his soldiers with a cry for orc blood. So maybe it'll be a black dawn.
FARMIR: [Going to the corpse of a dead Easterling and kicking it.] The enemy? His sense of duty was no less than yours, I deem. You wonder what his name is, where he came from, and if he was really evil at heart; what lies or threats led him on this long march from home; if he would not rather have stayed there, in peace. War will make corpses of us all.
It's easy for us to look at the orcs as unthinking beasts of pure evil. We can hate them and not care if they die. But Faramir pulls us back to reality. He tells Frodo and Sam that the journey of this single dead Easterling is completely unknown to them. Is he really that much different from any man in Middle-earth fighting against Sauron's army? When two soldiers lie dead next to each other on the field of battle, any idea of sides of good and evil seems irrelevant.