The Bible does not provide a formal “just war theory” as developed later in Christian history, but it does speak clearly about war, justice, and when taking up arms is righteous in God’s eyes. Scripture affirms that some wars are necessary for defending the innocent, executing God’s judgment, or preserving righteousness.
In the Old Testament, God directly commanded Israel to engage in certain wars. These were not for conquest alone but were acts of divine judgment against wicked nations. Deuteronomy 20 outlines the laws for warfare, including offers of peace before battle and the protection of civilians in some cases:
“When you go out to battle against your enemies… do not be afraid of them; for the Lord your God is with you…”
(Deuteronomy 20:1)
The wars against the Canaanites (Joshua 6–11) were commanded to remove deeply idolatrous and immoral peoples who had filled their measure of sin (Genesis 15:16). These were not indiscriminate or cruel, but just and directed by God.
David was a man of war, yet God still called him a man after His own heart (1 Samuel 13:14). He fought to defend Israel and uphold God’s covenant.
Ecclesiastes 3:8 affirms:
“A time to love, and a time to hate; a time of war, and a time of peace.”
In the New Testament, the focus shifts from national warfare to spiritual conflict, yet war itself is not condemned. Soldiers are not told to leave their profession but to act justly (Luke 3:14). Romans 13 affirms the state’s right to wield the sword to punish evildoers.
Jesus did not call for violent revolution, but neither did He oppose the idea of righteous justice. Revelation depicts Christ returning as a warrior king, executing judgment upon the wicked (Revelation 19:11–16).
A biblical view of just war includes:
Righteous cause (defense, judgment, or protection)
Legitimate authority (not vigilante action)
Moral conduct during war (not cruelty or excess)
Desire for peace, not glory or conquest
War in Scripture is never glorified but acknowledged as sometimes necessary in a fallen world to uphold righteousness and defend the innocent.