What a nation’s right to deploy force in self-defense actually means

On October 22, President Biden joined leaders from Western-allied countries in reaffirming Israel’s right to deploy deadly defensive force against Hamas, while also emphasizing the need to protect civilians. China later followed suit by similarly endorsing Israel’s right to self-defense. Some, including certain United Nations officials, disagree.

As the current conflict highlights, any exercise of trans-border force is bound to ignite fierce, frequently ideologically driven debates among government officials, legal scholars and the governments they sometimes advise. What is avoidable, however, is the prevailing bad habit of overcomplicating the international law of self-defense — a fault legal experts speaking to the media and to students unfortunately regularly commit.

This article will try to do better.

The simplest way to understand when a country can deploy justified defensive force, under customary international law and the UN Charter on which it is based, is through the lens of the more relatable and intuitive individual right to self-preservation under U.S. state law.

Often referred to as the “ancient right” or the “first civil right” in the context of individuals, the practices of ancient tribes (and later nations) concerning the use of defensive force has a long and tangled history. Both international and domestic law have default prohibitions against the use of force, yet they also create explicit carve-outs for when force is needed to stop or prevent a deadly attack.

­­­­­­­­­­­More specifically, under both American state self-defense laws and international law, an individual or country that is or about to be attacked (the “defender”) can successfully raise a self-defense claim by establishing that (1) the defender was the subject of an unprovoked violent attack; (2) the defender used an objectively reasonable degree of force to thwart the attack; and (3) the defender’s fear of serious bodily injury or death was both honestly held and objectively reasonable. We examine these basic elements in turn.

Necessity. Under both domestic and international law, the element of “necessity” makes defensive force available only when the central enforcement bodies, whether a domestic justice system or the UN Security Council, are not able to offer the defender adequate protection and there is no other way for the defender to be protected. The principle undergirding this element, in the international context enshrined in UN Charter Article 2(4), is that all human life is valuable and deserves protection, except when the country defending itself has no option but to resort to defensive force against those engaging in, or about to launch, an unjustified violent attack.

Imminence. Turning to the always-controversial issue of timing of the defensive force, both U.S. domestic law and international law require the attack to be either occurring or about to occur; that is, the attack must be ongoing or “imminent”. Debates rage in both the domestic and international law environments over what exactly constitutes an imminent — that is, an “about-to-happen” — attack. 

In the international context, many people have, not irrationally, become skeptical of the UN’s ability to effectively protect nations under attack. Some, including the governments of the U.S. (in the invasions of Iraq and Afghanistan), Russia (in the invasion of Ukraine), and Israel (in, among other situations, the Second Lebanon War), favor immediate anticipatory self-defense when they consider it necessary. They, accordingly, have called for a broader reading of Article 51, which provides that “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, until the Security Council has taken measures necessary to maintain international peace and security.”

Anticipatory self-defense. Those endorsing a more proactive vision of international self-defense emphasize that all defensive force, whether exercised by countries or individuals, is by definition “anticipatory” in that its aim is to avoid future harm. Any other reading, they contend, would require those being attacked to engage in acts of suicidal abstention.

It is worth noting that these arguments parallel those favoring greater access to proactive/anticipatory defensive force in the domestic law context of battered intimate partners; they should be able to kill, say, their violent sleeping drunken spouse to avoid a future, but not necessarily immediate, deadly assault when the spouse wakes up, rather than having to wait until that time or flee the residence.

Proportionality. Finally, under both domestic and international law, the force used must not be excessive. When a nation defends itself against an armed attack, the amount of force it deploys must from a means-ends perspective not be disproportionate to what is reasonably needed to achieve the legitimate defensive ends.

“Innocent shields.” President Biden and European Commission President Ursula von der Leyen have joined many other world leaders who allege that Hamas uses civilians as human shields by embedding themselves in civilian communities and taking civilians hostage. It is uncontroversial that an aggressor’s use of innocent shields is prohibited under domestic and international law and constitutes a serious war crime.

On the international stage, though subject to varying interpretations, the balance of authority holds that the presence of human shields does not prevent defensive force. Rather, an aggressor’s use of innocent human shields factors into the above-referenced proportionality calculations — the defending country must do everything feasible under the circumstances and take “active precautions” to avoid harming the civilian shields. That said, if the civilians are found to have used their civilian status to impede the defender’s actions they, like colluding shields in the domestic context, lose these protections.

It is unfortunate that many commentators tend to overcomplicate discussions of the international law of self-defense, too often shrouding public analysis in unnecessarily dense layers of legal theory. But the individual right to self-defense is a fairly intuitive pre-societal right that evolved separately from the state and that, in turn, provides the basis for a nation’s right to deploy defensive force.

As the present situation in the Middle East shows, there will always be factual and legal disagreements over how to apply the elements making up any particular claim of self-defense. But in times of crisis, the public deserves a clear, non-ideological and uncluttered explanation of the legal prerequisites that make up the foundational right to self-preservation under international law. 

Dr. T. Markus Funk, now in private practice, served as a federal prosecutor in Chicago and as a United States Department of State Section Chief in Kosovo. The author of a dozen books on criminal, comparative and international law, he teaches at the University of Colorado.