Comprehensive Answer to the Question:

"Prohibition of use of force under the United Nations Charter and the exceptions to it under
customary international law and state practice."

1. Introduction

The use of force in international relations is one of the most regulated areas under contemporary
international law, primarily governed by the United Nations Charter. The Charter, adopted in 1945,
emerged in the aftermath of the devastating world wars and was aimed at preventing further military
conflicts among states. Under the Charter, the use of force is prohibited as a general rule, with only two
explicit exceptions: self-defence under Article 51, and use of force authorized by the Security Council
under Chapter VII.

Despite this prohibition, customary international law and state practice have also shaped certain
exceptions and evolving doctrines, including humanitarian intervention, the Responsibility to Protect
(R2P), and pre-emptive self-defence. The legality and legitimacy of these practices remain controversial
and have been subject to intense judicial and scholarly scrutiny.

2. Prohibition of Use of Force: Article 2(4) of the UN Charter

Article 2(4) of the UN Charter states:

“All Members shall refrain in their international relations from the threat or use of force
against the territorial integrity or political independence of any state.”

This represents a jus cogens norm—a peremptory norm of international law from which no derogation is
permitted. The Nicaragua v. United States case (ICJ, 1986) confirmed the binding nature of Article 2(4) as
customary international law.

In that case, the International Court of Justice (ICJ) ruled that the U.S. had violated international law by
supporting the Contras in Nicaragua and by laying mines in Nicaraguan ports. The ICJ emphasized that
indirect use of force (such as arming rebels) is equally prohibited under Article 2(4).

The principle that sovereignty and territorial integrity must be respected lies at the heart of the
international legal order.

3. Exceptions to the Prohibition of Use of Force

a. Self-Defence under Article 51

Article 51 of the UN Charter provides:

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 “Nothing in the present Charter shall impair the inherent right of individual or collective self-
defence if an armed attack occurs against a Member of the United Nations...”

Key elements: - There must be an armed attack. - The self-defence must be necessary and proportionate.
- States must report the self-defence action to the Security Council.

In Oil Platforms Case (Iran v. USA, ICJ 2003), the ICJ reaffirmed the necessity and proportionality criteria as
central to the lawful exercise of self-defence. The Court held that use of force in response to isolated
incidents does not constitute a lawful act of self-defence.

In Legality of the Threat or Use of Nuclear Weapons Advisory Opinion (ICJ, 1996), the Court accepted
that the use of force in self-defence is permitted under international law but must be consistent with the
principles of humanitarian law.

b. Authorization by the UN Security Council (Chapter VII)

Under Chapter VII (Articles 39–42), the Security Council can authorize the use of force to maintain or
restore international peace and security.

Examples: - Kuwait Invasion (1990): UNSC Resolution 678 authorized the use of force against Iraq after its
unlawful occupation of Kuwait. - Libya (2011): UNSC Resolution 1973 authorized a no-fly zone and
protection of civilians in Libya, leading to military intervention.

Security Council-authorized interventions are considered legally valid exceptions to the general prohibition
of force.

4. Customary Law and Emerging Doctrines

a. Pre-emptive and Preventive Self-Defence

Though not expressly covered by Article 51, some states have claimed a right to pre-emptive self-defence,
particularly in light of modern security threats.

The Caroline Case (1837) remains the foundational precedent, stating that self-defence is lawful only if the
necessity is “instant, overwhelming, leaving no choice of means, and no moment for deliberation.”
This case established the principles of necessity and proportionality as part of customary international
law.

After 9/11, the U.S. National Security Strategy (2002) broadened the concept to include preventive self-
defence against emerging threats, particularly from non-state actors and rogue states.

However, the international community, including the ICJ in Armed Activities on the Territory of the Congo
(DRC v. Uganda, 2005), has remained cautious and often rejected overly broad claims of anticipatory self-
defence.

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b. Humanitarian Intervention

Humanitarian intervention refers to the use of force without Security Council authorization to prevent
widespread human rights abuses.

Examples include: - NATO’s intervention in Kosovo (1999) to prevent ethnic cleansing. Though lacking
Security Council authorization, the intervention was later described by the Independent International
Commission on Kosovo as “illegal but legitimate.”

Humanitarian intervention remains legally controversial due to the absence of explicit Charter-based
justification, but is occasionally tolerated when there is a clear humanitarian imperative.

c. Responsibility to Protect (R2P)

Endorsed by the 2005 World Summit Outcome Document, R2P recognizes that states have a duty to
protect their populations from genocide, war crimes, ethnic cleansing, and crimes against humanity. If
they fail, the international community can intervene, preferably through peaceful means, or as a last resort,
through force authorized by the Security Council.

While R2P provides a normative shift, it has not yet attained the status of customary law, and any
intervention must conform to existing Charter provisions.

5. Legal and Judicial Perspectives

a. Case: Democratic Republic of Congo v. Uganda (2005)

The ICJ held that Uganda’s military involvement in the DRC violated Article 2(4), and that no justification of
self-defence applied. The Court reiterated that cross-border armed attacks by non-state actors do not
automatically entitle the victim state to respond with force against another state’s territory.

b. Case: Nicaragua v. United States (1986)

The Court emphasized that supplying arms and logistical support to rebel forces in another state
constitutes unlawful use of force.

c. Legal Principle: Jus Cogens and Erga Omnes

The prohibition on use of force is considered a jus cogens norm, universally binding and overriding any
inconsistent treaty or custom. Breach of such norms triggers erga omnes obligations, meaning all states
have a legal interest in upholding the prohibition.

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6. Conclusion

The prohibition on the use of force under the United Nations Charter, especially Article 2(4), is a
cornerstone of the modern international legal order. The only clear legal exceptions are self-defence under
Article 51 and Security Council authorization under Chapter VII.

While evolving doctrines like pre-emptive self-defence, humanitarian intervention, and R2P represent
efforts to adapt to contemporary threats, their legal status remains uncertain and contested. Courts like
the ICJ have reaffirmed the narrow and cautious interpretation of these exceptions to preserve state
sovereignty, international peace, and the rule of law.

Therefore, any use of force not clearly grounded in Charter provisions risks being labeled as unlawful
aggression, triggering international condemnation and legal consequences.