We just entered the second year of a “era of persistent conflict” forecasted to extend to 2028. In that context, does it really matter if we can tell that a particular war has definitively concluded? Who gets to decide, and who should decide, how to calibrate a legal test to authoritatively determine the end of armed conflict? And how much guidance does current international law—the only normative regime that purports to be universal and uniform—actually provide as to when wars terminate?

We certainly do not lack for thorny factual situations. The Report on the Legal and Policy Frameworks Guiding the United States’ Use of Military Force and Related National Security Operations (December 2016) , for instance, that “[g]roups like al-Qa’ida are highly unlikely to disarm and sign instruments of surrender” and that the “unconventional” hostilities against such an enemy “presumably will not come to a conventional end.” Even where a peace deal does exist, it may be threatened before the ink dries, as the startling recent surge in in Colombia shows. More broadly, many contemporary “result in unstable cease-fires, continue at a lower intensity, or are frozen by an armed intervention by outside forces or by the international community. Hostilities, or at least acts of violence with serious humanitarian consequences, often break out again later.” (Of course, the underlying concern is not a challenge for only our time. Through the stark example of the period following what is conventionally considered the end of the American Civil War, scholar Gregory P. Downs that it was not always clear when earlier wars definitively ended either.)

Determining the end of an armed conflict often matters significantly. Many measures governed by the laws and customs of war—include killing and capturing the enemy, destroying and seizing enemy property, and occupying foreign territory, all on a possibly large scale—would usually constitute grave violations of peacetime law. In general, humanitarian actors have stronger to access civilian populations in need in relation to situations of armed conflict compared to other emergencies. And successful war-crimes prosecutions necessarily entail establishing the temporal parameters of a relevant conflict, because a war crime may be committed only in connection with an armed conflict.

In Indefinite War: Unsettled International Law on the End of Armed Conflict, a new for the Harvard Law School Program on International Law and Armed Conflict (HLS PILAC), we argue that international law, as it now stands, provides insufficient guidance to ascertain the end of many armed conflicts as a factual matter (when has the war ended?), as a normative matter (when should the war end?), and as a legal matter (when does the international-legal framework of armed conflict cease to apply in relation to the war?). The current plurality of legal concepts of armed conflict, the sparsity of international humanitarian law (IHL) provisions that instruct the end of application, and the inconsistency among such provisions (sometimes, even within a single legal instrument) thwart uniform regulation and frustrate the formulation of a comprehensive notion of when wars can, should, and do end.

In key respects, the guidance offered by IHL on the end of international armed conflicts (IACs) is far from clear. It contains provisions pertaining to several concerns—such as the release of prisoners of war or civilian internees and the conclusion of hostilities—using various formulations, such as “the general close of military operations,” “the cessation of active hostilities,” “the close of hostilities,” and “when peace is made.” In practice, many of those formulations have been subject to wide-ranging and conflicting interpretations. Additional debates surround whether armistices, which were traditionally used to suspend hostilities, have now transformed such that they are also capable of terminating a war. That disagreement could entail important consequences—possibly implicating, for instance, whether the 1953 Military Armistice effectively terminated (or not) the war on the Korean peninsula.

Non-international armed conflicts (NIACs) the most common type of contemporary armed conflict. Yet there are even fewer IHL provisions and rules concerning how those conflicts end. The primary judicially-sanctioned international-legal formulation on the end of applicability of IHL to NIACs a final and comprehensive “peaceful settlement” before IHL ceases to apply—a demand that will rarely be met for many NIACs today.

The difficulties in establishing the end of NIAC are especially relevant to U.S. jurisprudence and practice in the various purported armed conflicts against terrorist organizations. For instance, discerning whether conflict in Afghanistan and elsewhere continues is key to determining the legal power of the U.S. under international law to keep holding certain detainees at the Naval Base at Guantánamo Bay, Cuba—a question that has come before U.S. courts (and that has been briefed on ) repeatedly. Direct targeting in conjunction with these armed conflicts is another high-stake implication. Recall that the Obama Administration considered, as of December 2016, that the U.S. was engaged in armed conflict with certain terrorist organizations in (at a minimum) Afghanistan, Iraq, Libya, Somalia, Syria, and Yemen.

How will these particular conflicts end? The foundational end-of-war concern here—at least according to the Obama Administration—is the capacity of a terrorist organization to launch a strategic attack against the U.S. coupled with will to do so. In December 2016, the Administration assessed that al-Qaeda and ISIL “still pose a real and profound threat to U.S. national security. As a result, the United States remains in a state of armed conflict against these groups as a matter of international law….”

In light of the sparsity of legal doctrine in this particular area, we put forward, drawing from existing international law and scholarship, four theories on when a NIAC ends and when the international-legal framework of armed conflict ceases to apply in relation to it:

  • The two-way-ratchet theory (as soon as one of the constituent elements of the NIAC—sufficiently intense hostilities or sufficient organization of the non-state armed group—ceases to exist);
  • The no-more-combat-measures theory (upon the general close of military operations as characterized by the cessation of actions of the armed forces with a view to combat);
  • The no-reasonable-risk-of-resumption theory (where there is no reasonable risk of hostilities resuming); and
  • The state-of-war-throwback theory (upon the achievement of a peaceful settlement between the formerly-warring parties).

Under some of these theories, the Obama Administration’s position on the continuation of an armed conflict with terrorist organizations holds; on others, it fails. What approach the Trump Administration might take remains to be seen.

The stakes of being able to determine the end of conflict go well beyond the U.S. fight against terrorism. In today’s complex world of armed conflicts, we may be less likely to know armed conflicts when we see them. When, exactly, did the “Little Green Men” form (part of) a party to armed conflict in Ukraine? When do cyber operations give rise to an armed conflict? Not clearly knowing when an armed conflict begins, who the parties are, and how far the conflict extends geographically all frustrate, in turn, efforts to know when wars can, should, and do end.

Fleshing out the criteria for the end of war is a considerable challenge, and those looking to do so must address numerous concerns. Many of the problems we identify are first and foremost strategic and political. Yet, as part of a broader effort to strengthen international law’s claim to guide behavior in relation to war and protect affected populations, international lawyers must address the current confusion and inconsistencies that so often surround the end of armed conflict.