I have a million things to post in here but no time to comment on them.
From the Holy Scripture:
"I beg of you that when I am present I may not have to show boldness with such confidence as I count on showing against some who suspect us of walking according to the flesh. 3 For though we walk in the flesh, we are not waging war according to the flesh. 4 For the weapons of our warfare are not of the flesh but have divine power to destroy strongholds. 5 We destroy arguments and every lofty opinion raised against the knowledge of God, and take every thought captive to obey Christ, 6 being ready to punish every disobedience, when your obedience is complete."
- 2 Corinthians 10:2-6
" Then they came up and laid hands on Jesus and seized him. 51 And behold, one of those who were with Jesus stretched out his hand and drew his sword and struck the servant  of the high priest and cut off his ear. 52 Then Jesus said to him, “Put your sword back into its place. For all who take the sword will perish by the sword. 53 Do you think that I cannot appeal to my Father, and he will at once send me more than twelve legions of angels? 54 But how then should the Scriptures be fulfilled, that it must be so?”
- Matthew 26:50-54
"So Pilate entered his headquarters again and called Jesus and said to him, “Are you the King of the Jews?” 34 Jesus answered, “Do you say this of your own accord, or did others say it to you about me?” 35 Pilate answered, “Am I a Jew? Your own nation and the chief priests have delivered you over to me. What have you done?” 36 Jesus answered, “My kingdom is not of this world. If my kingdom were of this world, my servants would have been fighting, that I might not be delivered over to the Jews. But my kingdom is not from the world.”
- John 18:33-36
From early Christianity:
"But now inquiry is made about this point, whether a believer may turn himself unto military service, and whether the military may be admitted unto the faith, even the rank and file, or each inferior grade, to whom there is no necessity for taking part in sacrifices or capital punishments. There is no agreement between the divine and the human sacrament, the standard of Christ and the standard of the devil, the camp of light and the camp of darkness. One soul cannot be due to two masters—God and Cæsar. And yet Moses carried a rod, and Aaron wore a buckle, and John (Baptist) is girt with leather and Joshua the son of Nun leads a line of march; and the People warred: if it pleases you to sport with the subject. But how will a Christian man war, nay, how will he serve even in peace, without a sword, which the Lord has taken away? For albeit soldiers had come unto John, and had received the formula of their rule; albeit, likewise, a centurion had believed; still the Lord afterward, in disarming Peter, disarmed every soldier. No dress is lawful among us, if assigned to any unlawful action."
-Tertullian, Concerning Military Service
"You are a debtor to Him who cannot be deceived. You also have a debtor. God says to you: You are my debtor and he is your debtor. I do for you, my debtor, what you do for your debtor. You offer me a gift when you spare your debtor. You ask me for mercy: then do not be slow in showing mercy. Listen to what scripture says: I desire mercy more than sacrifice. Do not offer sacrifice without mercy, for your sins will not be forgiven unless you offer them with mercy."
- Augustine, Sermon 386 on Matthew 5 "Love your enemies"