Introduction
If the international order is to be more than parchment, it must rest on a principle that is both legally sound and morally intelligible: political communities have a right to defend themselves against armed attack. This claim is universal—no matter a state’s size, popularity, or politics—and it applies to countries whose conflicts are most visible today, including Israel and Ukraine. Recognizing the right is not the same as granting a blank cheque. Law and ethics place strict limits on how self-defense may be exercised. But the right itself is foundational. Without it, sovereignty is theater and human rights become unenforceable hopes.
The Legal Case
1) Sovereignty and the baseline prohibition on force
Modern international law begins with two paired rules: (a) states must not use force against the territorial integrity or political independence of other states (UN Charter art. 2(4)); and (b) a state retains an “inherent right” of individual or collective self-defense if an armed attack occurs (UN Charter art. 51). The second rule is not an exception that swallows the first; rather, it preserves the minimum capacity necessary for the first to mean anything. A prohibition on aggression would be incoherent if victims could not lawfully resist.
2) Customary law and the Caroline principles
Long before the Charter, customary law articulated two guardrails: necessity and proportionality. Self-defense must be necessary—responding to an actual or imminent armed attack—and proportionate—aimed at ending the attack and restoring security, not punishing or exacting vengeance. These limits remain the backbone of lawful defense today.
3) Collective self-defense
Because security is intertwined, states may assist a victim state at its request (collective self-defense). This recognizes that aggression against one can threaten many and that law need not force a victim to stand alone.
4) Non-state actors and the “unwilling or unable” problem
Attacks now often come from armed groups rather than regular armies. Many states and courts accept that large-scale attacks by non-state actors can trigger a right of self-defense, especially when the territorial state is unwilling or unable to prevent such attacks. This remains debated, but the core idea is continuous with the purpose of Article 51: the law protects people from violence irrespective of the attacker’s uniform.
5) Jus in bello still binds
Even when resort to force (jus ad bellum) is justified, the conduct of hostilities (jus in bello / international humanitarian law) remains strictly regulated: distinction (never deliberately target civilians), proportionality in attack, precautions, humane treatment of detainees, and prohibitions on collective punishment and forcible transfer. A lawful cause never sanitizes unlawful means.
The Moral Case
1) Natural-rights and social-contract reasoning
Political communities exist to secure basic goods—life, liberty, and ordered peace. If a state lacked the moral permission to repel violence, it would fail its most basic duty to its citizens. On a social-contract view, citizens yield certain powers to a state precisely so that common defense can be organized; denying the state the right to defend would betray that bargain.
2) Just War Theory
Just war thinking aligns closely with law: a defensive war is prima facie just if it repels aggression, is pursued with right intention (restoring peace, not revenge), has a reasonable chance of success, and is a last resort. Means must satisfy discrimination and proportionality. The moral right to self-defense is thus real, but it is not license; it is an assignment of responsibility under discipline.
3) Kantian and dignity-based arguments
Aggression instrumentalizes persons, treating them as means to political ends. Defense resists that instrumentalization and upholds the equal dignity of those attacked. A state that refuses to defend its people when it can is not morally “peaceful”; it is negligent.
4) Consequentialist considerations
Unchecked aggression invites more of the same. Allowing victims to defend themselves, and to receive assistance, reduces incentives for predation and helps stabilize expectations that borders and civilians are not fair game.
Universalism Means Symmetry
If the right is universal, it applies to friends and adversaries alike. We do not decide who may defend themselves by popularity polls, ideology, or sympathy. That symmetry is a feature, not a bug, of a rule-governed order. It constrains our biases and preserves the credibility of the law even when emotions run high.
Applying the Principles
Ukraine
Ukraine is the paradigmatic case of lawful and moral self-defense: its territory has been subject to large-scale invasion and occupation by a neighboring state. Ukraine’s resort to force to repel that aggression, and requests for outside assistance, fit squarely within Article 51 and just war criteria. The constraints still apply—Ukrainian operations must distinguish combatants from civilians and calibrate force to military necessity—but those constraints limit how defense is carried out, not whether Ukraine may defend itself. It may, and it should.
Israel
Israel faces recurrent armed attacks from organized groups that have launched rockets, raids, and other assaults. Under widely accepted readings of international law, such attacks can trigger Israel’s right to self-defense, including measures against the responsible armed groups even when they operate from adjacent territory. That right is real; the obligations are equally real. Israel must observe necessity and proportionality, take constant care to spare civilians, facilitate humanitarian assistance, and avoid collective punishment or forcible displacement. Affirming Israel’s right to defend its population is fully compatible with insisting that Israeli operations meet the strictest legal and moral standards—and with recognizing the rights and dignity of Palestinian civilians, who are themselves entitled to protection under the laws of war. Both truths stand together.
Addressing Common Objections
- “Self-defense is a pretext for aggression.”
Sometimes states misuse the language of defense. The cure is not to abolish the right but to enforce its limits: demand evidence of an armed attack or imminent threat; scrutinize necessity and proportionality; and maintain accountability for violations.
- “History or grievances negate the right.”
Historical injustices are morally weighty, but they do not negate a community’s present-tense right to be free from rockets, invasions, or hostage-taking. Remedies for historic wrongs must be pursued through law and diplomacy, not by tolerating new attacks on civilians.
- “Defense perpetuates cycles of violence.”
Unrestrained retaliation certainly can. Disciplined defense, constrained by law, can shorten wars by degrading the capacity for further attacks while preserving a diplomatic off-ramp. Peace is not achieved by forbidding defense but by binding it to rules and pairing it with credible negotiation.
- “Only nonviolence is moral.”
Nonviolence is admirable where it can protect the innocent. But when violent aggression is already occurring, refusing to defend may permit greater injustice. Moral seriousness requires meeting force that threatens innocents with proportionate, rule-bound resistance.
What the Right Does Not Entail
- It does not authorize punishment, annexation by conquest, or demographic engineering.
- It does not excuse war crimes, ever.
- It does not silence criticism of how force is used; on the contrary, scrutiny is part of honoring the right responsibly.
- It does not deny that adversaries’ civilians possess equal moral worth.
Conclusion
Every country possesses a legal and moral right to defend itself. International law codifies it; moral philosophy explains it; practical reason needs it. The right is universal and symmetrical, extending to states we favour and those we do not, and it comes paired with stringent duties that protect civilians and hold leaders to account. A world that denies Ukraine or Israel this right would not be more humane; it would be a world in which borders are invitations, civilians are bargaining chips, and law is rhetoric. The true path to peace is to uphold the right of self-defense—and the limits that give that right its legitimacy—consistently, publicly, and for everyone.