Just to add a couple of links with further reasoning on our discussion here
Did Jesus instruct his followers to buy a sword? If Jesus was telling them to have a sword handy (for self-defense) as they went into the world preaching the gospel, why then do Acts and the epistles consistently show the disciples accepting persecution peacefully? (Darrel Bock's commentary gives the following examples: Acts 4:25-31, 8:1-3, 9:1-2, 12:1-5).
read the rest in the link above.
The misuse of Romans 13:1-7, NIV Romans 13 has often been used to justify Christian support for war. The argument runs like this: as Christians, we are commanded in Romans 13 to obey our government. So if our government declares or supports a war, we are bound to support our government too.
There are at least three fallacies in that argument.
(see above link for the rest)