While scripture views war as a tragic result of human sin, it does not prohibit all violence or military service, distinguishing between unlawful murder and lawful defense or punishment.
The New Testament states that governing authorities are instituted by God to maintain justice and "bear the sword" against wrongdoers (Romans 13:1–4), giving the state—not private individuals—the legitimate right to use force.
Neither John the Baptist nor Jesus told soldiers or centurions to abandon their military profession; instead, John told them to be content with their wages and avoid extortion (Luke 3:14)
Based on scriptural principles, theologians and commentators outline core biblical requirements for a war to be considered morally permissible:
Legitimate Authority: Waged only by proper government leadership, not vigilantes or individuals.
Just Cause: Focused on defending the innocent, stopping direct aggression, or restraining severe evil.
Last Resort: Pursued only after diplomacy, peace terms, and nonviolent options fail.
Right Intention: Fought out of a duty to protect rather than a desire for selfish gain, vengeance, or conquest.
(Sorry to copy and paste but can't be bothered to write it out myself)