An Option for ECOWAS?: The Legality of Treaty-Based Regional Organization Military Intervention Under the Jus Ad Bellum (Part I)

An Option for ECOWAS?: The Legality of Treaty-Based Regional Organization Military Intervention Under the Jus Ad Bellum (Part I)

[Captain Peter S. Konchak is a Judge Advocate in the United States Army who is currently assigned to the Office of the Staff Judge Advocate for III Armored Corps and Fort Cavazos, and whose academic work is focused on matters of national security law and policy.]

[The views expressed in this article are those of the author and do not represent the Department of Defense, the Department of the Army, or any other entity or agency of the U.S. government.]


Over the summer, a military junta deposed the democratically elected government of Niger in a coup d’état. In response, the Economic Community of West African States (ECOWAS), a regional bloc of which Niger is a member, resolved to take “all measures necessary”—which “may include the use of force”—to restore constitutional order” in Niger.

As of this writing, ECOWAS has not undertaken any such forcible action. Nevertheless, in its most recent statement on the political situation in Niger, it has indicated that the military intervention option remains on the table.

ECOWAS has not publicly articulated a clear international legal justification for its contemplated intervention. Critically, however, it has authorized the deployment of an ECOWAS military force to Niger for purposes of “restoring constitutional order” in that country, and has subsequently described that authorization as a decision to “activate the clause providing for the application of legitimate force” in Niger.

Those statements suggest that ECOWAS may rely upon the military intervention provisions in the 1999 Protocol to the ECOWAS Revised Treaty as the basis for any use of force against Niger. Under that protocol, ECOWAS is empowered to conduct an armed intervention against one of its member states in the event of an actual or attempted overthrow of a democratically-elected government.

That possibility implicates an important and underexplored aspect of international law—the legality, under the jus ad bellum, of a military intervention conducted pursuant to an explicit, treaty-based mechanism authorizing the use of force by a regional organization against one of its member states. Part I of this article concludes that, in general, a military intervention conducted on that basis is lawful. Part II further concludes that, in particular, an ECOWAS intervention in Niger conducted pursuant to the military intervention provisions of the ECOWAS Treaty would be legal under the jus ad bellum.

The Use of Force Prohibition and Intervention by Invitation

The contemporary jus ad bellum broadly proscribes the interstate use of armed force, a prohibition enshrined in Article 2(4) of the U.N. Charter and widely recognized as a jus cogens norm of customary international law. A “use of force” is broadly understood to encompass any unconsented-to projection of military force by one state against another. The only universally-recognized exceptions are where force is employed in individual or collective self-defense, or pursuant to U.N. Security Council (UNSC) authorization. Those norms apply to regional organizations as well as individual states.

Nevertheless, in accordance with the concept of “intervention by invitation,” the use of military force in another state is lawful if it is sanctioned by a governmental authority that exercises effective control over the territory and population of that state. Often, such consent is provided on an ad hoc basis immediately preceding the use of force. Pursuant to general state responsibility principles, however, a state may also consent to an armed intervention on its territory “in advance by treaty.”

In accordance with the fundamental rule of pacta sunt servanda, a state generally remains bound to perform its duties under a treaty for so long as it remains a party to that agreement. All other things equal, therefore, an operative treaty provision authorizing a regional organization to engage in military intervention in one of its member states can legally justify such an intervention absent the ad hoc consent of that state.

Nevertheless, many scholars contend that a military intervention that is clearly and contemporaneously opposed by a government which exercises effective control constitutes an unlawful use of force, irrespective of whether it is otherwise authorized under a treaty.

According to this view, preventing a state from contemporaneously rejecting a military intervention to which it had previously consented would effectively strip the state of its autonomy as a sovereign state. Further, while a state can consent to the use of force on its territory, a state is not competent to authorize the use of armed force against its territory or interests, as such an intervention is necessarily coercive. Moreover, since the non-use of force norm has the status of jus cogens, two or more states cannot agree that a coercive intervention by one of them against the other will be lawful a between themselves. Finally, this view also advances the proposition that a treaty provision which allows a regional organization to engage in coercive intervention against one of its member states is void under Article 103 of the U.N. Charter because it conflicts with Article 53 requirements for regional enforcement action.

The Nature of the Use of Force Prohibition

A jus cogens norm is a rule of international law from which no derogation is possible—states cannot “contract around” the general rule in their mutual relations. Thus, two states cannot agree to authorize the slave trade or piracy as between themselves. An international agreement in which two states agree to recognize an otherwise-illegal use of force by one of them against a third state as lawful would similarly be void.

The use of force prohibition, however, is unique insofar as the content of that proscription directly relates to the sovereignty of the state that is the object of the use of armed force.

A valid, ad hoc “intervention by invitation” is lawful because the projection of military force by the intervenor is authorized by the entity that exercises the sovereignty of the state that is subjected to that use of force. This indicates that the interstate use of armed force is unlawful only when it violates the sovereign right of the target state to exercise absolute authority over the use of force within its borders. In other words, the use of force prohibition is implicated when the state’s monopoly on legitimate violence is contested by another state—when another state challenges its ability to effectively regulate or constrain the use of physical force on its territory by both domestic and foreign actors.

Accordingly, the ability of states to alter the specific circumstances in which the non-use of force norm applies inter se must be understood in the context of how states may alter their particular sovereign rights and obligations by international agreement.

As a definitional matter, one of the fundamental competencies of a sovereign state relates to the ability to limit its otherwise-absolute authority over all persons, things, and activities within its territory via its intercourse with other states. Indeed, a sovereign state can voluntarily relinquish its sovereignty under an international agreement. A state can, for example, agree to be absorbed by another state.

Accordingly, a sovereign state must necessarily possess the capacity to accept restrictions upon—or even cede completely—its otherwise-exclusive authority to regulate the use of armed force within its territorial boundaries by means of international agreement. In those circumstances, the parties to that agreement do not derogate from the use of force prohibition. They do not agree that either party is allowed to lawfully infringe upon another state’s exclusive right to authorize the use of force in its territory. Instead, they structure their sovereign rights and obligations vis-à-vis each other so as to alter the circumstances in which the authority to control the lawful employment of armed force within either or both of their territories is exclusive to one of them.

Likewise, as a function of its sovereignty, that competency must encompass the capacity to accept binding limitations on the state’s otherwise-exclusive authority over the use of force within its territorial jurisdiction. Binding international obligations of that kind may indeed limit the discretion of a state’s future governments to decide upon another state’s use of force on its territory. Such duties do not, however, limit the autonomy of the state itself, as their acceptance by the state’s present governmental authority involves the exercise of sovereignty. As alluded to above, all states are competent to enter international agreements that may circumscribe their latitude for engaging in future conduct. 

Importantly, the content and structure of the U.N. Charter supports the conclusion that armed intervention carried out pursuant to a valid treaty provision is lawful because it falls outside of the use of force prohibition.

The contemporary prohibition on the interstate employment of armed force was first established in the 1928 Kellogg-Briand Pact, which proscribed “recourse to war for the solution of international controversies” and as “an instrument of national policy.” As the International Military Tribunal for Germany (IMT) explained in its Nuremberg Judgment, the Pact made it illegal for any state to engage in armed conflict with another state except for purposes of self-defense.

Under the U.N. Charter, that customary prohibition is codified in Article 2(4), which is subject to two treaty-based exceptions. Article 51 reiterates the core customary exception of self-defense. Article 42, however, further provides that states may lawfully utilize force against another state pursuant to UNSC authorization. This did not codify any recognized exception to the customary non-use of force norm, but created a separate basis for the lawful use of armed force as between U.N. member states.

Accordingly, while under the Charter, Article 42 enforcement action is an exception to Article 2(4), it does not constitute an exception to the customary non-use of force norm. Yet UNSC enforcement action authorized is invariably recognized as lawful—states do not deem the use of armed force against a U.N. member state pursuant to UNSC authorization as a violation of the customary prohibition on the non-defensive employment of interstate armed force.

The most logical explanation for such practice is that states recognize that U.N. member states, through their adoption of Article 42, have agreed that under certain circumstances they may be subjected to a use of force that would otherwise infringe upon their authority to regulate the use of armed force on their territories. Accordingly, Article 42 is viewed as an international agreement that brings UNSC enforcement action outside the scope of the non-use of force norm, because U.N. member states have ceded their authority to regulate the use of armed force within their territories to the UNSC in those situations.

U.N. Charter Article 103

Similar considerations also demonstrate that a treaty-based intervention mechanism does not implicate Article 103 of the U.N. Charter, which provides that a U.N. member state’s obligations under the Charter “shall prevail” if they conflict with that state’s duties under another international agreement.

Under U.N. Charter Article 53, “no enforcement action shall be taken under regional arrangements or by regional agencies” absent UNSC authorization. Many scholars have concluded that those terms conflict with a treaty provision that authorizes a regional organization to use armed force on the territory of one of its member states without that state’s contemporaneous consent. For those scholars, an intervention of that kind would constitute “enforcement action” insofar as it involves a use of force that is actively contested with military means by the state that is the object of the intervention.

The problem with those interpretations, however, is the predicate assumption that any military intervention that is resisted with armed force by the target state necessarily constitutes “enforcement action” under the U.N. Charter. But that is probably inaccurate.

As discussed, while UNSC enforcement action is an exemption from the customary non-use of force norm, it is an is an exception to Article 2(4). Under the terms of the Charter, therefore, “enforcement action” refers to a use of armed force that otherwise violates Article 2(4) but is rendered lawful because it is authorized by the UNSC. It describes a situation in which the relevant use of force would infringe upon the target state’s authority to regulate the use of force within its borders had that state not agreed to accept limitations on that authority pursuant to Article 42.

By contrast, a use of force that is authorized in accordance with an intervention mechanism contained in a separate international agreement constitutes an exemption from both the customary use of force prohibition as well as Article 2(4). An intervention conducted pursuant to that separate provision does not implicate Article 2(4), because the target state has consented to the relevant use of force outside the terms of the Charter, and therefore does not constitute “enforcement action.”

The Legality of Regional Treaty-Based Intervention Mechanisms

The foregoing indicates that a military intervention conducted by a regional organization against one of its member states pursuant to a provision of its constitutive treaty will, in general, be lawful under the jus ad bellum. Part II of this article will evaluate that conclusion in the context of ECOWAS’ contemplated use of force against Niger, assessing whether ECOWAS and other relevant international actors have accepted ECOWAS’ treaty-based regional intervention mechanisms as a legitimate jus ad bellum authority for an ECOWAS military intervention against one of its member states.

Part 2 of this post will be found here.

Photo attribution: UN, ECOWAS partners kick-off Western Accord 2016” by U.S. Army Southern European Task Force, Africa is licenced under CC BY 2.0 DEED.

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