War and Christianity are incompatible.
A person need only tell himself about a bad deed that although he knows that the deed is bad, it is impossible to avoid doing it—a person need only tell himself this, and he will commit the most terrible atrocities, and not only will he think that such things are permitted, he will even be proud of them. One of such atrocities is war.
If armed peace and war are to be ever eliminated, then it will not be done by the kings and the strongmen of the world. War is too profitable for them. War will only end when those who suffer the most from war realize that their fate is in their own hands and use the simplest and most natural means to liberate themselves from the miseries of war: cease obeying those who are dragging them to war and making them soldiers.
— After Harduin
To those who, without understanding our faith, want us to take arms and to kill people for the sake of a common cause, we can answer: “Your pagan priests, who are attached to your idols and your temples, keep their hands clean so that the sacrifices which they bring to your gods could be performed by hands that are clean and undefiled by blood and murder. Regardless of what kind of war might break out, you will never enroll them into the army. If this custom is wise, then would it not be even wiser for us Christians to keep our hands clean from any defilement?”
When we encourage people with our exhortations not to transgress the unions and conditions of the world, we are much more useful to the rulers than their wars. We are truly taking part in the works whose aim is the common good when to our exhortations we add contemplations and exercises that teach people how to free themselves from their passions. Yes, we fight more than everyone else for our emperor. Granted, we do not serve under his standards and will not do so even if he tries to force us, but we fight for him with good deeds.
— Origen
Jesus has laid the foundation for a new society. Before him, the people belonged to one or many masters, as herds belong to their owners. The princes and the strongmen of the world pressed down on the people with the full weight of their pride and greed. Jesus puts an end to this disorder, raises the bowed heads and frees the slaves. He teaches them that, being equal before God, people are free, that no one can hold power over his brothers by himself, that equality and freedom, the divine laws of humankind, are inviolable; that power cannot be a right; that in the social order it is a duty, a service, a kind of slavery, which is accepted freely for the sake of the common good. Such is the society that Jesus is establishing. Is this what we see in the world? Is this the teaching that reigns on earth? Are the princes the slaves or the masters in our world? For nineteen centuries, generation after generation keep passing down the teaching of Christ and claiming to believe in it, and has anything changed in the world? The nations, oppressed and suffering, are still waiting for the promised liberation, and not because the word of Christ is untrue or invalid, but because the people have either not understood that the realization of the teaching must be accomplished by their own efforts, by their steadfast will, or, having fallen asleep in their humiliation, they did not do the one thing that leads to victory, they are not willing to die for the truth. But they will awaken. Something is already stirring among them; they hear a voice that says: salvation is near.
— Lamennais
A human being in general, and a Christian in particular, must not participate in war and in preparations for it, neither personally, nor financially, nor by reasoning about it.
