International law, primarily enshrined in the UN Charter, generally prohibits the use of force by states. This prohibition is a cornerstone of the international legal order, aimed at maintaining peace and security. However, there are two narrowly defined exceptions where the use of force is permissible: self-defense and authorization by the UN Security Council. Self-defense can be individual or collective, responding to an "armed attack." The Security Council, acting under Chapter VII of the UN Charter, can authorize force to maintain or restore international peace and security, often in response to threats to peace, breaches of peace, or acts of aggression. Controversial concepts like anticipatory self-defense and humanitarian intervention (Responsibility to Protect - R2P) are debated but not universally accepted as standalone justifications for unilateral force without UNSC authorization.

Relevant Statutes and Sections:

• UN Charter, Article 2(4): Prohibits the threat or use of force against the territorial integrity or political independence of any state.
• UN Charter, Article 51: Preserves the inherent right of individual or collective self-defense if an armed attack occurs, until the Security Council has taken necessary measures.
• UN Charter, Chapter VII (Articles 39-42): Empowers the Security Council to determine threats to peace, breaches of peace, or acts of aggression and to take measures, including the use of force, to maintain or restore international peace and security.

Important Landmark Cases:

• Nicaragua v. United States (ICJ, 1986): Clarified the definition of "armed attack" for the purpose of self-defense under Article 51, emphasizing that it must be of a certain gravity and scale. It also distinguished between the most grave forms of the use of force and other less grave forms.
• Oil Platforms case (ICJ, 2003): Further elaborated on the requirements for self-defense, including the necessity and proportionality of the response to an armed attack.

Clear Conclusion: The use of force in international relations is strictly limited to self-defense against an armed attack and actions authorized by the UN Security Council. These exceptions are interpreted narrowly to uphold the fundamental principle of non-use of force and prevent arbitrary military interventions.