Over-the-Horizon Operations – Part II: Where May Force Be Used?


| Dec 20, 2021

Over-the-Horizon - Part II

Part I of this series examined the issue of when the United States would enjoy a legal right to conduct over-the-horizon (OTH) operations. It identified three bases for such operations: UN Charter Chapter VII authorization or mandate, self-defense, and request from the government of the State into which they are conducted.

However, even though a decision to mount an OTH operation may be lawful, there must be a legal basis for conducting the operation in the location concerned. This second installment in the series explores the question of when the United States may penetrate the sovereign territory of Afghanistan to carry out such an operation. The question loomed large during this month’s Naval War College workshop on Afghanistan and international law hosted by the Stockton Center for International Law.

OTH Operations as “Internationally Wrongful Acts”

An OTH operation into Afghanistan—whether launched from outside that nation, conducted from within Afghan national airspace, or executed through a boots-on-the-ground operation—would potentially breach international law. Three “internationally wrongful acts” (the term for unlawful activities in the law of State responsibility) are likely candidates: a violation of Afghan sovereignty, coercive intervention into that State’s internal affairs, and the wrongful use of force against Afghanistan.


The most obvious “internationally wrongful act” would be a violation of Afghanistan’s sovereignty. It is a long-standing rule of international law that States shoulder an obligation to respect the territorial sovereignty of other States. As observed by the Permanent Court of Justice in the 1927 Lotus Case, “the first and foremost restriction imposed by international law upon a State is that—failing the existence of a permissive rule to the contrary—it may not exercise its power in any form in the territory of another State” (para. 45). Any time a State’s military forces conduct operations into another State’s territory, as envisioned during OTH operations, the right of sovereignty is implicated.


States also enjoy the international law right to be free from “intervention” into their internal affairs by other states. In its Paramilitary Activities judgment, the International Court of Justice (ICJ) opined that every use of force equally qualifies as intervention. In my estimation, this is a questionable assertion because, as the Court observed, intervention requires coercive intrusion into the target state’s domaine réservé (internal or external affairs) (para. 205). “Coercion,” as the term is understood in the context of the intervention rule, refers to action intended to cause a State to act in a manner it would not otherwise act or refrain from taking measures that it would otherwise take.

While most uses of force are coercive, motives other than coercive intent can also inspire them. For example, the objective of an OTH operation into Afghanistan might be to compel the Taliban to terminate support of a non-State group that has conducted hostile operations against the United States, as was the case in 2001. That operation would qualify as coercive. But an OTH operation might also be calculated solely to strike directly at the non-State group rather than force the Taliban to take any particular action. Indeed, most U.S. drone attacks against terrorists have not been designed to change the behavior of the State into which they have been conducted; instead, they were intended to remove a threat directly.

Use of Force

The third potential internationally wrongful act implicated by OTH operations is the use of force. Article 2(4) of the UN Charter and customary international law prohibit the use of force by one State against another. The question is whether the fact that an OTH operation at the requisite level of severity (see discussion in Part I) unfolds on Afghanistan’s territory is, standing alone, enough to qualify it as a use of force against that State. The law is unsettled.

By one view, the operation would be a use of force regardless of whether it is directed at the Taliban or a non-State group present in Afghanistan. That a State has used force on Afghan territory is the determinative fact. This view would appear to be supported by the 1974 Definition of Aggression Resolution, aggression being, according to the Resolution, “the most serious and dangerous form of the illegal use of force.” Article 3(b) of its annex provides, “Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State.” And Article 3(e) indicates that when the forces of one State are consensually in another but engage in activities inconsistent with that consent or remain beyond the termination of the agreement, the first State has engaged in aggression. By the definition, the intentional non-consensual presence of combat forces on a State’s territory is a wrongful use of force.

An alternative view is that an action must be “against” the State concerned to qualify as a use of force; the mere fact that force is used “on” the State’s territory is not sufficient to constitute a use of force against the territorial State. By this interpretation of the prohibition, any OTH operation targeting persons or objects because of their affiliation with Afghanistan would qualify, but a surgical strike having no nexus to Afghanistan beyond its location would not. A paradigmatic example would be attacking a non-State group that operates from Afghan territory for its own purposes and without the support of the Taliban.

A critical question in applying this analysis is whether the Taliban constitutes the government of Afghanistan such that an attack on it or affiliated forces would amount to the use of force against Afghanistan. As explained in Part I of this series, the Taliban are the de facto government of Afghanistan for the purpose of holding Afghanistan responsible under international law. This being so, the better, albeit not definitive, legal interpretation treats them as the government vis-à-vis the use of force prohibition. A use of force against the Taliban would therefore be one against the State of Afghanistan.

Whatever position one takes on the open questions regarding intervention and the use of force, it is undeniable that an OTH operation would at least violate Afghanistan’s sovereignty. The status of the Taliban as its government has no bearing on this characterization, for status as a State and status as a government are separate legal matters. It is the former that is at issue in territorial sovereignty matters. The next question, therefore, is whether a justification exists in international law for an operation that would otherwise be unlawful.

Circumstances Precluding Wrongfulness

International law recognizes various “circumstances precluding wrongfulness”; these “secondary rules” of international law render an otherwise unlawful action by a State lawful. In the case of OTH operations, they may sometimes preclude the wrongfulness of operations into the territory of Afghanistan.

The UN International Law Commission has set forth the circumstances that preclude wrongfulness in its Articles on State Responsibility (ASR), a nonbinding but highly influential restatement of the law of State responsibility: consent, self-defense, countermeasures, force majeure, distress, and necessity (arts. 20-25). Technically, they justify the non-performance of a legal obligation owed by one State to another, such as the obligation to respect other States’ sovereignty or even, in cases of self-defense, to refrain from using force against them.

Chapter VII Authorization or Mandate

Part I of this series examined the effect of Security Council resolutions under Chapter VII of the UN Charter. Although the International Law Commission did not cite Security Council authorizations or mandates contained in such resolutions as a circumstance precluding wrongfulness, the instruments would have that effect. By Article 25 of the Charter, “the members of the United Nations agree to accept and carry out the decisions of the Security Council in accordance with the present Charter.” Lest there be any question as to the primacy of that obligation, Article 103 provides, “In the event of a conflict between the obligations of the Members of the United Nations under the present Charter and their obligations under any other international agreement, their obligations under the present Charter shall prevail.” The Article 25 obligation would equally displace most customary international law obligations. Indeed, Article 59 of the ASR makes this point by providing, “These articles are without prejudice to the Charter of the United Nations.”

Accordingly, a Security Council resolution under Chapter VII would prevail over obligations to respect sovereignty and the prohibitions against intervention and the use of force. And resolutions allowing operations by “all necessary means” (see Part I) would implicitly include OTH operations into Afghanistan’s territory if they contributed to achieving the resolution’s objective.

This would be so even if the Taliban objected, unless the text of the Council’s resolution barred territorial penetration in the absence of State consent.  Indeed, lack of consent distinguishes Chapter VI operations (peacekeeping) from Chapter VII actions (peace enforcement). Therefore, such a resolution could allow OTH operations against the Taliban, groups affiliated with the Taliban, or groups having no connection to the Taliban. The presence of U.S. weapons, weapons systems, or personnel in Afghanistan would not violate international law unless the OTH operation somehow exceeded the four corners of the resolution and no other basis for being in Afghanistan, such as self-defense, existed.


Article 20 of the ASR provides, “Valid consent by a State to the commission of a given act by another State precludes the wrongfulness of that act in relation to the former State to the extent

that the act remains within the limits of that consent.” Thus, a lawfully consented-to OTH operation into Afghanistan would not violate Afghan sovereignty or constitute intervention or use of force against that State. Consent could be granted both with respect to a group against which Afghanistan is conducting operations, like ISIS-K, or as to a group with which only the United States is engaged in hostilities. As explained in Part I, the legal basis for the former would be an Afghan request for assistance, whereas self-defense would allow for operations against the latter. But in either case, the consent would preclude any wrongfulness of mounting the operation into the country.

The question is who wields authority to consent to an action that would otherwise breach an international law obligation owed to the State of Afghanistan. By August 15th, the Taliban had captured the Presidential Palace in Kabul, and on September 13th, in testimony before Congress, Secretary of State Blinken described the Taliban as the “de facto government” of Afghanistan. As discussed in Part I of the series, the ASR Commentary observes, “A general de facto Government … is itself an apparatus of the State, replacing that which existed previously” (p. 49). It refers to the 1923 Tinoco Concessions Arbitration, in which the arbitrator, Supreme Court Chief Justice and former President Taft, pointed to the determinative factor: “The question is, has [the group concerned] really established itself in such a way that all within its influence recognize its control, and that there is no opposing force assuming to be a government in its place?” (p. 382). In that case, the actions of the Tinoco government, which had unconstitutionally seized power in 1917, bound Costa Rico following the 1919 demise of that government. By this view, which prevails in international law, de facto Taliban control over the instruments of governance entitles it to act on behalf of the State in granting consent to U.S. OTH operations.

Note that representatives of the new Islamic Emirate of Afghanistan have not replaced Islamic Republic of Afghanistan officials at the United Nations or other international organizations. This raises the question of whether the former government retains any authority to consent to OTH operations. Retention of such authority is possible during an international armed conflict in which one of the parties to the conflict is in belligerent occupation of the other’s territory, and the latter maintains a government-in-exile; occupation is a care-holder function pending return of the occupied State’s government once the conflict ends.

But it remains unsettled whether a government-in-exile can exist during a non-international armed conflict and, if so, whether that status requires control of any territory. The better view is that there is no government-in-exile analog in cases of non-international armed conflict once the former government loses control of most territory and the instruments of governance. Thus, consent by former Afghan officials to conduct OTH operations into the country would be unlikely to preclude the wrongfulness of crossing into Afghan territory to conduct OTH operations.

It must be cautioned that, as is clear from the text of Article 20, the Taliban de facto government would enjoy the right to frame consent as it wished. For instance, it might consent to OTH operations only against a specific group, only in a particular geographic area, only involving the use of particular weapons systems, or only on a case-by-case basis.


No such limitations apply to operations based on the right of self-defense found in Article 51 of the UN Charter and customary international law. Part I of this series described when States enjoy the right to self-defense. The question here is whether self-defense in the form of an OTH operation may be conducted into Afghanistan.

Article 21 of the ASR provides, “The wrongfulness of an act of a State is precluded if the act constitutes a lawful measure of self-defense taken in conformity with the Charter of the United Nations.” Self-defense is designed to allow the victim State of an “armed attack” to resort to forcible actions to defend itself against the attack. It necessarily contemplates cross-border action because violence qualifying as an armed attack will always have a transnational element. Equally, to the extent that self-defense may preclude the wrongfulness of using force in another State, it self-evidently does so for lesser internationally wrongful acts, including violation of sovereignty and engaging in coercive intervention.

If the Taliban conducts the armed attack, and is treated as the de facto government of Afghanistan, OTH operations into Afghanistan against the group would be lawful. Similarly, if a non-State group has conducted hostilities at the armed attack level against the United States “on behalf” of the Taliban or with its “substantial involvement” (see Part I), OTH operations into Afghanistan against either that group or the Taliban would enjoy the benefit of self-defense as a circumstance precluding wrongfulness.

The challenging question is whether the United States may conduct operations into Afghanistan without the consent of the Taliban against groups that have engaged in hostilities against the United States at the armed attack level. The question only arises if one accepts the argument that the right of self-defense extends to armed attacks mounted by non-State actors, an issue examined in Part I, and a view that I support.

This is a fraught question in international law. Some States (see, e.g., France in the context of cyber operations) and scholars are of the view that such operations are impermissible. For them, either sovereignty is a veil that cannot be pierced, or the use of force is a peremptory norm to which circumstances precluding wrongfulness do not apply according to Article 26 of the ASR.

Arguments beyond this article’s scope could be raised in support of and against this position. For instance, there is a reasonable debate about whether the use of force is a peremptory norm in the first place, such that Article 26 would bar actions into a State that was not responsible under the rules for attribution for the armed attack that triggered the right to self-defense.

In my estimation, the appropriate approach when international law rights collide is to seek an interpretation that best accommodates their object and purpose. The State that is the victim of an armed attack has an undeniable interest in defending itself effectively. Still, the territorial State into which the OTH operation is launched has a compelling interest in maintaining its sovereign prerogatives over activities on its territory.

In the immediate aftermath of 9/11, I, along with other scholars (see, e.g., Yoram Dinstein’s “extra-territorial law enforcement”), began to assert that forcible defensive actions into another State against a non-State group were permissible where the territorial state was “unwilling or unable” to address the situation (as they generally would be obliged to attempt to do according to the due diligence rule). The United States eventually adopted the approach, explaining in 2016,

Under international law, a State may use force on the territory of another State in self-defense only if it is necessary to do so in order to address the threat giving rise to the right to use force in the first instance. States therefore must consider whether actions in self-defense that would impinge on another State’s sovereignty are necessary, which entails assessing whether the territorial State is able and willing to mitigate the threat emanating from its territory and, if not, whether it would be possible to secure the territorial State’s consent before using force on its territory against a non-State actor.

As noted, the unwilling or unable approach only works if a State enjoys a right to self-defense against an armed attack by a non-state group. Even assuming, as I do, that States have that right, they must exercise it in accordance with the conditions of “necessity” and “proportionality” that States universally accept and the ICJ has repeatedly acknowledged (Paramilitary Activities, para. 176; Oil Platforms, para. 73; Armed Activities, para. 147). At issue in unwilling or unable situations is the first condition, necessity.

Necessity requires that there be no viable alternative to force to defeat the armed attack. Given that the State acting in self-defense must accommodate the sovereignty interests of the State into which it will conduct the operation, the former must first demand that the latter take measures to put an end to hostile operations from its territory and give it an opportunity to comply that is consistent with the attendant circumstances. In the case of Afghanistan, the United States would have to allow the Taliban to take steps against the non-State group before the OTH operation may be mounted, at least so long as giving the Taliban the opportunity to do so is feasible in the situation at hand. If the Taliban is unwilling or unable to act, the necessity test has been satisfied. Of course, the OTH operation would still have to meet the other requirements for self-defense discussed in Part I.


Part I of this series examined when the United States has the right to use force taking the form of an OTH operation. This second installment has taken the analysis one step further by assessing where the United States may exercise such a right. The final contribution to the series will address the law that would govern how such operations must be conducted.​


Michael N. Schmitt is the G. Norman Lieber Distinguished Scholar at the United States Military Academy. He is also Professor of Public International Law at the University of Reading, Strauss Center Distinguished Scholar and Visiting Professor of Law at the University of Texas, and Professor Emeritus at the United States Naval War College.