The U.S. Should Communicate in the Jus ad Bellum Lexicon to Strengthen Its Deterrence Posturing

Editor’s Note: In a previous post related to this topic, the authors argue the U.S.’s reliance on the Rules of Engagement has failed to provide strong legal bases for its threats to use force in self-defense.

Deterrence has always been a central pillar of American foreign policy and national security objectives. The United States has traditionally rested on its nuclear and conventional arsenal coupled with economic power to enable its deterrent posture. Competition between states and non-state actors has expanded into new domains like space, the sea bed and the electromagnetic spectrum. The law, too, in its regulation of these domains has increasingly become a contested space. In this environment, the effectiveness of U.S. efforts to deter its adversaries is declining. While the United States has largely unrivaled military power compared to its state competitors, it often struggles to communicate the legal basis for its use of force. It is in this legal and policy context that we argue for deliberate use of the jus ad bellum lexicon and paradigm by policymakers to create and communicate more effective deterrence policies and take decisive actions that comply withdomestic and international law. Using the recent escalating tensions between the U.S. and Iran as an example, this post highlights how the jus ad bellum better supports deterrence signaling. 

To the detriment of its deterrence goals, the United States has consistently failed to communicate clear deterrent signals to its adversaries. The U.S. has incoherently shifted between legal paradigms in its threats to use force in response to recent Iranian aggression, often using general self-defense terminology or U.S. Rules of Engagement (ROE) language in its messages. Despite shared terminology, ROE “self-defense” has different standards and consequences for a target than self-defense under jus ad bellum, jus in bello or international human rights law. (For an in-depth overview of self-defense across the use-of-force paradigms, see our first post on this topic.) With a uniquely U.S.-centric meaning, ROE “self-defense does not translate well to international audiences and thus does not provide clear deterrent signaling, even when unambiguously identified as the source of authority. This is amplified by the fact that the key mission-specific rules are classified and cannot be used in threats to establish a strong deterrent posture. More importantly, ROE self-defense is inherently reactive and limited: It requires some actor to first demonstrate hostile intent or commit a hostile action, and only then may the U.S. actor, circumstances permitting, respond with force. That response must attempt to deescalate the situation—pursuit and capture are generally not authorized if the hostile actor disengages. Thus, not only are its complex standards and confusing terms U.S.-specific, use of the ROE in strategic messaging implies a self-limiting response and locks the United States into a peacetime paradigm that surrenders escalation control to the adversary. In contrast, the jus ad bellum has none of these defects. 

For a threat to be effective, it must be clear, credible, legitimate and backed by the capacity to act. Clarity ensures an adversary’s precise comprehension of the threat. This comprehension, including an understanding of the legal paradigm upon which the deterring state acts, is required so that the adversary can evaluate the cost of a promised consequence. Credibility relates to the adversary’s belief that the threatening party has both the capacity and the willingness to act as promised. Inextricably tied to legitimacy, credibility is rooted in sound legal bases that foster international and domestic approval for uses of military force. It is only when these elements coalesce with the other pillars of national power, forcing the adversary to weigh the benefits of their actions against the threatened costs, that effective deterrence can be achieved. 

Deterring malign Iranian action and influence is explicitly central to the United States’s National Security Strategy. Doing so, in part, involves issuing credible threats to employ the instruments of national power—including the use of military force—to discourage aggressive Iranian policies and behavior. But due to past reliance on the ROE and incoherent shifts between legal lexicons, the U.S. has consistently failed to convey credible threats and send deterrent signals to its adversaries. Most recently, the Department of Defense again struggled to articulate the condition in which U.S. warships may legally use force when they (and others) are threatened at sea. In April, Iranian vessels harassed U.S. ships in the Arabian Sea, and the president tweeted threats to use force in response. Attempting to clarify the presidential tweets, the Defense Department offered an ambiguous explanation that referenced ROE concepts of hostile act and the inherent right to self-defense. (For an in-depth analysis of the application of the U.S. ROE to the Iranian speedboat provocations, see this article.) Problematically, invocation of the peacetime rules for the use of force signals to the world that the U.S. would not be justified in attacking Iranian vessels for their harassing activities. It correspondingly weakens the U.S. deterrence posture by raising doubt about U.S. willingness to make the high-cost commitment to use force under jus ad bellum. The U.S. should instead frame its threat signals in terms of the jus ad bellum in order to craft strategic messaging in a manner that enhances its deterrent posture.

Explicit and exclusive use of the jus ad bellum lexicon would reduce ambiguity in U.S. communications to its adversaries, including Iran, thereby increasing U.S. legitimacy and restoring U.S. control over when and how hostilities escalate into an armed conflict. These benefits are consistent with modern deterrence theory and accordingly provide the best chance for the U.S. to actually influence Iran’s behavior. For three reasons we will discuss below—improved clarity, increased legitimacy and escalation control—the United States should explicitly incorporate jus ad bellum terminology and/or outright reference to the paradigm by name in its strategic messaging.

Deterrence Theory and Iran

The United States acknowledges that deterrence in today’s world is significantly more complex than during the Cold War. However, the fundamentals of deterrence theory as developed during the Cold War are still applicable today. In January, Secretary of State Mike Pompeo explained the concept of deterrence as follows: 

In strategic terms, deterrence simply means persuading the other party that the costs of a specific behavior exceed its benefits. It requires credibility; indeed, it depends on it. Your adversary must understand not only do you have the capacity to impose costs but that you are, in fact, willing to do so.

Implicit in Pompeo’s statement is that effective deterrence requires clearly communicating (or signaling) to the target both the capacity to carry out the military action and the willingness to do so. This communication can be explicit or implicit. For instance, a state may threaten to use force explicitly through official statements or implicitly through the positioning of its military forces near the adversary. “Credibility” refers to the degree to which the adversary believes the threatening state is truly willing to use force. Lastly, “capacity” refers to the state’s actual ability to carry out the threat. While the United States enjoys an unquestionable advantage over Iran across all pillars of traditional national power—and therefore America’s capacity to decisively engage the Iranian Navy is not in doubt—the U.S.’s perceived willingness to use force is dubious due to the ambiguity of its threats. This stems in part from the vague and shifting legal bases for the threatened use of force.

As Pompeo describes, an effective threat must make the target decide that the benefits of pursuing its present course of action are not worth the costs if the threat is carried out. Linking the derrent message to a target state’s vital interests is thus critical in crafting an effective threat. In the case of Iran, the Defense Intelligence Agency outlined Tehran’s vital interests in a 2019 assessment of Iran’s military power, stating: 

Iran has consistently demonstrated a preference for using partners, proxies, and covert campaigns to intervene in regional affairs because of limitations in its conventional military capabilities and a desire to maintain plausible deniability, thereby attempting to minimize the risk of escalation with its adversaries. 

This conclusion is also supported by a Rand Corp. study from 2019 that found:

the broad consensus within the [government of Iran] is that Iran should have a strong military and the capabilities to deter enemies and raise the costs of conflict. Fundamentally, Iran’s defense posture is based on deterrence.

Put another way, Iran’s aggressive actions at sea are an attempt to project strength, signaling to its adversaries a credible and high-cost response to any state that would challenge Iran. Tehran aims to deter such actors from attacking Iran, without actually escalating into an open war.

Projecting strength while avoiding open conflict is a prime national objective for Iran. Therefore, Iran must maintain control over if and when a situation escalates. By crafting threats to Iran with the jus ad bellum lexicon, the United States can convincingly signal its commitment to use force against Iran in open conflict, depriving Tehran of escalation control. While simultaneously conveying the legality and legitimacy of a threatened use of force, the jus ad bellum paradigm also produces beneficial strategic ambiguity (discussed in detail below) as to the scope of a U.S. response to Iranian aggression. However, it avoids the detrimental ambiguity as to whether a response will actually occur that is produced by other paradigms, and is thus more likely to achieve the desired

[…]

Read the original article: The U.S. Should Communicate in the Jus ad Bellum Lexicon to Strengthen Its Deterrence Posturing