Violence, War and Just War Theory
What Do Religions Say About Violence?
Most religious traditions do not treat violence as morally neutral. They recognise that life has value and that harming others requires serious justification. Yet they also acknowledge that the world is not always peaceful, and that believers must think carefully about when, if ever, force is permissible. This tension between the ideal of peace and the reality of conflict runs through all the major world religions.
Christianity teaches that human beings are made in the image of God, and that taking life is therefore a grave matter. Jesus said in Matthew 5:43–44: “Love your enemies and pray for those who persecute you.” This command to love even enemies is central to the Christian ethic of nonviolence. However, many Christians have also concluded that some forms of force can be justified in extreme circumstances — the tradition of Just War Theory emerged precisely to answer that question.
The prophet Micah taught that one day nations would “beat their swords into ploughshares and their spears into pruning hooks” (Micah 4:3). This verse is widely used in religious peace traditions to describe the ideal of a world without war. It appears in the Hebrew scriptures and is cited across Jewish and Christian traditions alike.
Terrorism and Religion
Terrorism is the deliberate use of violence against civilians to cause fear and achieve political or ideological ends. The causes of terrorism are complex: they include political grievances, economic marginalisation, cultural humiliation, and extremist ideologies that claim divine sanction for violence. Religious extremism is one factor, but sociologists and security analysts stress that it is rarely the only cause.
The relationship between religion, politics and terrorism in the 21st century is deeply contested. Acts of terror have been committed in the name of Christianity, Islam, Judaism and other faiths, yet the overwhelming majority of believers in each tradition condemn terrorism absolutely. Religious leaders across traditions have consistently argued that targeting innocent civilians is never justified and that extremist groups misuse and distort their scriptures. For example, mainstream Islamic scholars argue that the killing of innocent non-combatants is strictly forbidden under Islamic law, and that terrorist groups who claim religious legitimacy have abandoned the authentic teaching of their tradition.
Just War Theory
Just War Theory is the most influential framework Christians have used to think about war. The medieval philosopher and theologian Thomas Aquinas drew together earlier ideas and identified three core conditions for a just war in his Summa Theologiae: first, the war must be declared by a legitimate authority (not a private individual); second, there must be a just cause (such as defence against aggression); and third, the warriors must have a right intention (seeking peace and avoiding personal gain or cruelty).
Thomas Aquinas outlined three conditions in the Summa Theologiae: (1) legitimate authority — only a ruler with responsibility for the common good can declare war; (2) just cause — the cause must be the defence of the innocent or righting a grave wrong; (3) right intention — the aim must be to achieve good or avoid evil, not to satisfy ambition or hatred. Later Catholic tradition expanded these into a fuller set of criteria found in the Catechism of the Catholic Church (CCC 2309), adding principles such as last resort, proportionality, and a reasonable chance of success. Protestant traditions have generally adopted similar criteria. An important but distinct concept is jus in bello (justice in the conduct of war) — the idea that even a just war must be fought in a just manner, sparing non-combatants and avoiding disproportionate destruction.
Holy War
Holy War is a concept found across traditions. In the Hebrew Bible, passages such as Joshua 8:1 describe God commanding the Israelites to fight and promising victory. In early Christian history, the Crusades were presented as holy wars to reclaim Jerusalem. The concept of holy war differs from Just War in that it claims divine authorisation rather than depending on moral criteria. Most modern religious thinkers are deeply uncomfortable with the idea of a war that claims God’s direct command, partly because it has historically been used to justify atrocities.
Just War Theory requires war to meet morally rational criteria such as just cause, legitimate authority and right intention. Holy War claims direct divine command and is not assessed by the same rational conditions. Many modern religious thinkers reject Holy War as too easily abused, while accepting that Just War criteria may sometimes permit defensive force.
Conventional warfare involves armies engaging one another directly on battlefields. Just War criteria were developed with this kind of conflict in mind. Technological warfare, including drone strikes and “surgical” precision attacks, raises new moral questions: is a strike on a single target that risks civilian casualties ever proportionate? Does removing the human cost from one side change the moral calculus? Religious ethicists disagree. Some argue that precision weapons can actually reduce civilian deaths and are therefore more just; others argue that the ease of using remote weapons lowers the moral threshold for violence.
Apocalyptic warfare, most seriously represented by nuclear weapons, challenges Just War Theory fundamentally. The indiscriminate destruction of nuclear bombs makes it impossible to distinguish combatants from civilians, and the scale of potential harm means no military objective could be proportionate. Many religious traditions, including many Catholic bishops and Quaker communities, have argued that nuclear weapons can never be used justly and have called for disarmament. The book of Joel 3:9–11 was used in early Christian debates about war: “Beat your ploughshares into swords and your pruning hooks into spears” — ironically reversing Micah’s vision of peace into a call for battle, illustrating how scripture can be read in contrasting ways.
Religious Responses to War
Different religious communities and denominations respond to war in different ways. Most agree that peace is the ideal and that war should be a last resort. Many Christians point to Jesus’s teaching in Matthew 5:43–44 — “Love your enemies” — as a reason for caution about any resort to violence. Others emphasise the responsibility to protect the innocent and argue that allowing evil to go unchecked is itself a moral failure. Islamic teaching, similarly, affirms that life is sacred and that taking it unlawfully is among the most serious sins, yet it also recognises the legitimacy of defending the community against aggression. Both traditions therefore contain threads of both nonviolence and regulated force.