It may only be one sentence long, but Article 2(4) of the UN Charter has been described as a "cornerstone of modern international law" — and its bright red line.

It prohibits countries from threatening or using force against another state's territory or political independence. Drafted in the aftermath of World War II, its objective was to maintain peace and make negotiation — not armed conflict — the default mode to settle disputes. 

Article 2(4) has since often been invoked in major geopolitical crises — from Ukraine to the Middle East — with actors on opposing sides interpreting it from their perspectives. 

Among the grounds cited by the United States and Israel for their recent "pre-emptive" strikes against Iran on February 28 were the need "to restrict its ballistic missile program" and "end its support of terrorist groups." 

Critics counter that these grounds did not fall within the UN Charter's exceptions, noting that only specific UN organs — above all the Security Council — can authoritatively determine when force is lawful. 

In January 2026, UN special rapporteurs condemned the US intervention in Venezuela, in which US troops captured Venezuelan president Nicolas Maduro, as a "grave" and "deliberate" breach of Article 2(4).

It also prompted United Nations Secretary General, Antonio Guterres, to warn that around the world "the rule of law is being replaced by the law of the jungle."

The phrase that tried to outlaw war

Before 1945, there was no general rule that prohibited states from using force. Wars raged and there were limited institutions to prevent conflict.

Repeated failures to restrain aggression in the early 20th century — culminating in two world wars — convinced states that peace required a binding, enforceable rule against unilateral force.

The UN Charter was signed on June 26, 1945, in San Francisco, becoming the foundational treaty that created the United Nations and bound its members to a new legal framework for maintaining global peace.

At its core was Article 2(4), which reads: "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, or in any other manner inconsistent with the Purposes of the United Nations."

It effectively prohibited the use of force with only two exceptions: self‑defence in response to an armed attack (Article 51), and the use of force authorized by the UN Security Council. It became the Charter's central mechanism for preventing powerful states from resorting to force whenever they saw fit.

It should also be noted that the Charter did not specify "force" to include pre‑emptive strikes, humanitarian intervention or regime change. These would later become contested points in justifying the use of force.

The grey zones of the anti-force UN article

Article 2(4) used broad terms such as "use of force" and its "threat" based on the warfare technology known back then. Today, cyber operations can disable infrastructure or disrupt essential services, and drones can deliver precision strikes across borders without putting their operators in harm's way. When these operations cause destruction or disruption similar to a conventional attack, they are widely understood to fall under Article 2(4). But if actions stay below that threshold, like data theft or espionage that cause no widespread physical damage, the rule is moot. 

A second grey zone concerns when a state may use force in self‑defence. Article 51 allows this only after an "armed attack," a term the Charter uses to describe a significant, violent assault of the kind associated with mid‑20th‑century warfare.

Many modern operations — cross‑border raids, targeted killings, cyber intrusions and drone strikes with limited physical effects — may not amount to an "armed attack" in the sense required to trigger self‑defence. Furthermore, the self‑defence concept also raises questions of necessity and proportionality, as seen in reactions to Israel’s response to the October 7, 2023 Hamas terrorist attacks: Israel clearly had a right to defend itself, but the scale of its operations has prompted debate. The ICJ case whether Israel has been or is committing genocide against the Palestinian people in Gaza is still pending.

And finally, there's the structure of the Security Council. Article 2(4) promises sovereign equality, yet the Council gives the five veto-wielding permanent members — the United States, United Kingdom, Russia, China and France — extraordinary power to determine when force is lawful. When the Council is paralyzed by any of their vetoes, states have sometimes acted alone and justified their actions afterwards. 

At the axis of major conflicts

Article 2(4) sits at the center of many of history's contentious military confrontations, some of which are listed below:

Iraq’s invasion of Kuwait (1990)

Iraq's sudden occupation and attempted annexation of Kuwait in August 1990 was condemned within hours by the UN Security Council, which demanded Iraq's withdrawal and later authorized force to reverse the invasion, even without explicitly invoking Article 2(4). Baghdad insisted that Kuwait was historically part of Iraq and accused it of economic sabotage, but neither argument provided a lawful basis for crossing an international border with military force.

NATO's intervention in Kosovo (1999)

Though contested for its lack of legality, NATO's 1999 air campaign in Kosovo is often remembered as a humanitarian intervention aimed at stopping large‑scale atrocities against Kosovar Albanians. Proponents argued that doing nothing would have allowed ethnic cleansing to continue. Yet the operation was launched without Security Council authorization and without any claim of self‑defence; thus "technically" contravening Article 2(4). The Independent International Commission on Kosovo later described it as "illegal but legitimate," underscoring the tension between humanitarian necessity and the Charter's strict prohibition on the use of force.

US‑led invasion of Iraq (2003)

The United States, the United Kingdom and coalition partners invaded Iraq in March 2003 without new Security Council authorization. Washington and London argued that Iraq's alleged weapons of mass destruction (WMD) posed an imminent threat and that earlier Gulf War resolutions implicitly allowed renewed force. These claims failed to gain broad international support, and UN inspectors had not confirmed the existence of WMDs. After the invasion, it became clear that the central factual premise — that Iraq possessed active WMD programs — was unfounded, further undermining the legal justification.

UN Secretary‑General Kofi Annan later stated that the intervention was "not in conformity with the UN Charter."

Russia's full‑scale invasion of Ukraine (2022)

Russia's war in Ukraine triggered widespread condemnation, with the UN General Assembly calling for withdrawal and the International Court of Justice finding that Russia's "genocide‑prevention justification" had "no plausible basis." 

Moscow claimed that Ukraine was committing genocide against Russian‑speaking people in the Donetsk and Luhansk regions without credible evidence, and that it was using force to stop it as humanitarian necessity. Neither argument was accepted by UN bodies or by most states.

Edited by: Sarah Hofmann