Jus ad bellum refers to the body of international law that governs the conditions under which states may lawfully resort to war or the use of armed force. It is a critical component of the broader field of international humanitarian law, but distinct from jus in bello, which regulates how war is conducted.

1. Core Principles of Jus ad Bellum

The modern framework of jus ad bellum is primarily rooted in the United Nations Charter, particularly:

• Article 2(4) – Prohibits the threat or use of force against the territorial integrity or political independence of any state.
  Read Article 2(4) of the UN Charter
• Article 51 – Recognizes the inherent right of individual or collective self-defense if an armed attack occurs.
  Read Article 51 of the UN Charter

These articles establish a presumption against the use of force, making it illegal unless justified by one of the two primary exceptions:

1. Self-defense
2. Authorization by the UN Security Council under Chapter VII of the Charter
   Chapter VII – Action with Respect to Threats to the Peace, Breaches of the Peace, and Acts of Aggression

2. Just War Criteria

Historically, just war theory influenced jus ad bellum. Modern interpretations of just cause include:

• Self-defense (in response to an armed attack)
• Humanitarian intervention (controversial and often unauthorized under international law)
• Collective security (as mandated by the UN Security Council)

Additionally, five criteria often inform assessments of lawful war initiation:

1. Just cause
2. Right intention
3. Proper authority and public declaration
4. Last resort
5. Probability of success and proportionality

These elements, while not codified, help guide ethical and legal evaluations of military action.

3. Emerging Challenges

Contemporary debates around jus ad bellum include:

• The legality of pre-emptive self-defense or anticipatory strikes
• Cyberattacks as a form of armed attack
• Humanitarian interventions without UN approval, as in NATO’s 1999 Kosovo campaign

These issues reflect the evolving nature of conflict and the need for ongoing interpretation of international norms.

4. Conclusion

Jus ad bellum remains a cornerstone of international law aimed at preserving global peace and limiting war. It balances the sovereign right of states to defend themselves with the international community’s interest in preventing unnecessary or illegal uses of force.

For further reading:

• International Committee of the Red Cross (ICRC) – The Law of Armed Conflict
• Oxford Public International Law – Use of Force
• UN Audiovisual Library – Jus ad Bellum