There is fundamentally something wrong with the world. For whatever reason, humans have always believed--regardless of culture, religion, or location--that we are to be an active part of the solution. Whenever this marring evil is identified or personalized, something must be done and that something is always war.
In 300, the war is against slavery, tyranny, and ingloriousness. The Spartans believe that, at least to some degree, they hold this. They have perpetual peace because they train for perpetual war. The Persians represent hubris, barbarism, and the end of the Spartan way of life--they are the bringers of slavery and tyranny. So the leader of the Spartans, Leonidis, sets out with 300 of his best men to meet the massive Persian army in full combat, to rid Greece of evil and protect freedom.
The overtones to the current American situation in the Middle East, or looking back to the Soviet Union era, are obvious, even if they may not be intentional. You cannot tell a story about a people rising in violence against an enemy that threatens their very way of life in this age without hearing the subtle undercurrents about terrorism, 9/11, or another ruthless Asian regime. If the battle is not engaged, the only outcome will be loss of life, liberty, and property...or so it seems.
As others have said better than myself, war always leads to loss of liberty, no matter what side you are on. Governments never back down and get rid of "emergency measures," nor do they shrink the size of their armies and navies, nor does the propoganda machine ever stop. With victory comes insecurity; there is always some other convining not-like-us group that is waiting in the wings to take the position as king of the hill. Hence perpetual war for perpetual peace. The idea itself that violent conquest leads to peace is itself an old piece of propoganda that in the hands of the powerful becomes a call to honorable war, but in the hands of the powerless is known as crime, rebellion, or treason.
This is not to say, though, that negotiations always (or ever) work. There will always be madmen (and women) who will not listen to reason, or be empathetic, or what have you. There will always be those who have a never-ending thirst for blood. Or power. Or victory. Or security. These people cannot and will not be stopped by force of words alone. Whatever happens to be fundamentally wrong with the world, it is foolish to believe that it will listen to reason. Or that it will agree to your definition of reason to begin with.
In a broken, sinful, violent world, war is inescapable.
I have been a pacifist for a number of years now. I've been called illogical, a coward, looked at as "less than American," and generally ignored. That is because pacifism has been confused with cowardice and compromise. While I do not agree with many things that they said or did, I look to Martin Luther King Jr. and Gandhi and wonder what they would have thought (or what they did think!) of such an assessment. To be a pacifist does not mean the denial of war, but instead a different assessment of how victory is to be accomplished.
The Messiah was supposed to be a great military leader, like Joshua, or David, or Ehud, or... He was supposed to throw off the pagan yoke and crush, with the force of God Himself, all pretentions to Israel's place in God's plan--as Adam, as ruler of the beasts that the pagans had turned themselves into. The war was with the Caesars and once Rome, the embodiment of the Serpent, was torn down, then the sons of God would rule in wisdom, prosperity, and with peace. However, Jesus did not do this. It is not because he had a great love for the Romans--he considered having one of their coins idolatrous and an affront to the true God. It was not because he hated his countrymen--his tears were always to gather the people to himself and to God. It was because he saw that the war being fought (at that time) coldly was the wrong war.
While we were watching 300 I asked Bethany when she thought that the Persians soldiers would start defecting over to the Spartans. She responded that they were slaves. Exactly. A slave is forced to do what they do not because of love or loyalty, but because of compulsion. They do the will of the master, whoever that master might be. I thought that they would see the victories of the Spartans over the Persians (free men versus slaves) as a reason to defect, to become free, and to fight against their old masters. That did not happen in the movie, partly, I surmise, because slaves are given limited vision. They cannot see freedom by changing allegiances, but only freedom through the destruction of the other. This is the doctrine that they are fed by their masters and it is impossible to not believe it. Worse when one master pits two sets of slaves against each other.
The problem wasn't the Romans, just like it isn't the Iraqis, or the Iranians, or any other number of "incarnations of evil." The problem isn't the slaves, it is the masters. Whereas his comtemporaries saw the Romans as the great, gnashing, Danielic beast, Jesus saw them as pawns of that beast, the accuser, the evil one, the first serpent and last dragon, the one known in Hebrew as the satan. Yes, the Romans had to be defeated, but by changing loyalties, not bloodshed. The satan had to be crushed and his weapon is always violence and death. Jesus didn't deny the war, he denied the way it was to be fought and the terms that would be used.
Leonidis, instead, perpetuated the circle of violence. His attack on Persian would necessitate a counter-attack, which would provoke a counter-attack, and so on, until one (or both) groups were decimated to historical and cultural irrelevance. The war would go on in different guises until the whole world was at each others' throats. The battle was won, but the enemy was not disarmed.
Jesus, by submitting to death--to the fulness of God's curse and the full power of Caesar and satan--defeated it, because it had no legal claim on him. He triumped by taking the very weapons out of the hands of the enemy and parading them around as paltry, restoring them to the place of servants to his people instead. That is why martyrdom is honorable; because death is defeated in resurrection--both Jesus' in the past and his peoples' in the future.
So, the pacifist has a toolbox full of weapons at his disposal, but none are carnal or "of this world", instead we fight with the resurrection of Jesus and overcome by resisting to play evil's game. The only lasting victory, or sustainable peace, can be won this way: by overcoming evil with good.