America, Iran, and “Anticipatory Self-Defense”: International Legal Standards of Presidential War-Making Decision
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America, Iran, and “Anticipatory Self-Defense”: International Legal Standards of Presidential War-Making Decision

“Any attack by Iran on anything American will be met with great and overwhelming force. In some areas, overwhelming will mean obliteration.”-US President Donald Trump, June 23, 2019

“The United States has great strength and patience, but if it  is forced to defend itself or its allies we will have no choice but to totally destroy North Korea with fire and fury.”- US President Donald Trump, Speaking at UN General Assembly (2017)


If push comes to shove, any US presidential decision to attack Iran would likely be based upon some notion of lawful preemption or “anticipatory self defense.” The right of national self-defense, both anticipatory and post-attack, is a “peremptory” or jus cogens norm under international law. This is not to suggest that pertinent legal standards would in some significant way actually determine the cost-effectiveness or rationality of any such American military action, but only that they would be conveniently invoked after the fact, as a more-or-less appropriate retroactive justification.

Realistically, launching a defensive first strike against Iran would stem solely from various American operational considerations. To be sure, it would be better if US foreign policy making were authentically mindful of relevant law, but any such principled expectation in the “Trump Era” would be sorely naive.

This means, inter alia, that even if supportive criteria for anticipatory self-defense could be discovered in pertinent international law, any considered preemptive strike that had seemingly poor odds of tactical success would be dismissed out of hand. In this connection, moreover, it would be difficult to expect promising odds of tactical success so long as Trump continues to claim that “I need no exit strategy” and to remain distant from the intellectual antecedents of “escalation dominance.”

In any upcoming crisis with Iran concerning preemptive US military force, the president would face a simultaneous obligation to dominate escalation processes and avoid catastrophic war. This obligation, furthermore, would need to be contextualized within a re-emergent bipolarity between the two original superpowers – that is, between the United States and Russia.

On all such vital policy matters, the critical facts are both plain and daunting. Already, it is unreasonable to expect that a preemption against Iran could plausibly succeed. In part, at least, this is due to what Carl von Clausewitz famously called “friction,” or the difference between “war on paper” and “war as it actually is.” Rather, beyond any reasonable doubt, the probable costs of any such strike would exceed the probable gains. Among other things, therefore, a preemptive first strike by the United States against Iran would likely be irrational.

Notwithstanding the evident primacy of strategy and tactics, an American president should remain fully aware of all related legal considerations. But before he could ever manage this gainfully heightened level of awareness, he would first have to clarify much more precisely what he is after in Iran. Accordingly, is he “simply” seeking the right to inflict certain more-or-less proportionate harms upon Iran if that state should once against shoot down an American drone or become tangibly responsible for some similar “unfriendly action?” Or, as he has been musing publicly, is Mr. Trump thinking primarily about preventing a nuclear Iran, and staving off that understandably fearful development at all apparent costs?

Right now, of course, it’s hard to tell. After all, as had been the case earlier with North Korea, the president’s assorted comments concerning American security vigilance are less than specific and very conspicuously disjointed.

What next?  To begin, Mr. Trump and his policy counselors will need to better understand and further elucidate their specific military objectives vis-à-vis Iran. Here, considerations of law will necessarily follow more fundamental considerations of objective.

There is more. International law is never a suicide pact. Designed, in its coherent totality, to ensure the safety of states in an anarchic and conflict-driven “Westphalian” world, its binding or “peremptory” rules include the “inherent” right of individual and collective self-defense. After the seventeenth century (1648) Peace of Westphalia, which ended the Thirty Years’ War and created our anarchic legal system of independent states. At times, this national prerogative may be exercised not only after an armed attack has already been suffered (the legal expectation codified at Article 51 of the UN Charter, a treaty to which the US is an original party), but also, on occasion, in advance.

What more exactly are these exceptional permissible times? The answers to such such questions are potentially urgent for US President Trump to master, especially in the persistently ambiguous case of Iranian nuclear weapons development. Is Tehran expanding its efforts in such a palpably worrisome development? If so, are these expansions in any verifiable violation of authoritative international law, or even prospectively genocidal (in view of expressed Iranian regime statements calling for the destruction of Israel), or are they now genuinely allowable – perhaps in part because of a prior and willful US Trump withdrawal from the 2015 JCPOA agreement?

In examining such complex matters, analysts may reason from the general to the particular. What does world law say about preemption in general? Here, complexity includes the possible convergence of genocidal crimes and “crimes against humanity,” which antedate the conventional criminalization of genocide. Although the settled rules of the UN Charter  reserve the right of self-defense exclusively to states that have already suffered an armed attack, an equally valid customary legal norm may still permit a first use of force if  the danger posed is “instant, overwhelming, leaving no choice of means and no moment for deliberation.” The essential significance of a norm’s customary character under international law is that the norm binds even those states that are not parties to the pertinent codifying instrument or convention. Drawn from an 1837 incident in military history known as the Caroline  (concerning the unsuccessful rebellion in Upper Canada against British rule), this usually inconspicuous doctrine builds upon the foundational seventeenth-century legal writings of jurist Hugo Grotius.

Self-defense, proclaims the Dutch scholar in The Law of War and Peace (1625), may be permitted “not only after an attack has already been suffered, but also in advance, where the deed may be anticipated.”  In his later text of 1758, The Right of Self-Protection and the Effects of Sovereignty and Independence of Nations, Swiss jurist Emmerich de Vattel similarly affirms: “A nation has the right to resist the injury another seeks to inflict upon it, and to use force and every other just means of resistance against the aggressor.”

But where is there any discoverable evidence that Iran seeks to “inflict injury” upon the United States? Even if such evidence were capably produced by the Trump White House, any subsequent US defensive strikes would still need to meet the standard “Law of War” criteria of “discrimination,” “proportionality” and   “military necessity.” In other words, even a US invocation of “anticipatory self defense” would not automatically allow President Trump an operational carte blanche in fashioning any allegedly remediating uses of American force.

International law has multiple, overlapping and sometimes even contradictory sources. Significantly, article 51 of the UN Charter, limiting self-defense to circumstances following an armed attack, does not override the equally valid customary legal right of anticipatory self-defense.  As for customary international law in general, it is most prominently explained at article 38 of the (UN) Statute of the International Court of Justice. The actual conditions under which an expression of anticipatory self defense could conceivably be lawful require enemy threats that are “instant,” “overwhelming” and “imminent in point of time.”

Unsurprisingly, assessing these criteria in any particular setting or decisional circumstance could prove overwhelmingly subjective.

I first taught international law at Princeton in 1970. While I was still a “working professor” of international law, I instructed my students at the very first course lecture about the importance of “Article 38.” One can only hope that today, Donald Trump’s legal advisors have some sense of this importance themselves.

There is more. In rendering this country’s indispensable strategic judgments, President Trump and his advisors should expressly recall the US Constitution and certain assorted US Supreme Court decisions. Both sources proclaim unambiguously that international law is part of the law of the United States. This “incorporation” dates back to the eighteenth century English common law, which quickly became the literal foundation of subsequent US law.

In reaching verdicts, state courts applied this “law of nations” even prior to adoption of the Constitution, and it was well familiar to most participants at the Federal Convention. While the current President of the United States cannot recall the title of a single book he has read apart from the Bible, the Framers were more or less learned in the complex jurisprudential treatises of Grotius, Pufendorf and Vattel.

Jurisprudentially, in this country, the times have very surely changed.

The US Constitution stipulates at Article 6, inter alia, “…all treaties made or which shall be made….shall be the supreme law of the land.” The confirming Supreme Court case here is the Paquete Habana (1900). In still broader connections, William Blackstone’s seminal Commentaries became the principal foundation of all early United States law. Incontestably, his Commentaries on the Law of England effectively represented the original legal system of the United States.

Moreover, the Federalist Papers, especially No. 3 (Jay), and Nos. 80, 82 and 83 (Hamilton) clearly reference the universal authoritativeness and worldwide jurisdiction of international law.

To wit, Chief Justice John Marshall declared that all international law, whatever its source, was binding upon the courts of the United States

To be in compliance with his own oath of office, President Trump  must finally understand international law an integral part of US law, and, correspondingly, as similarly binding.

In connection with US President Donald Trump’s plans for a presumptively nuclearizing Iran, there remains one more important clarification . The Caroline case decision makes an implicit distinction between preventive war (which is never legal) and preemptive war, which can conceivably be lawful. As a justification for military action, anticipatory self-defense is never permitted to protect one’s state against some merely emergent threat, and is potentially permissible only when the “danger posed” is judged both “instant” and “overwhelming.”

Using such a classical jurisprudential framework, it is doubtful that this US president could presently construct even a minimally valid legal argument for preemption against Iran. This would be the case even if the considered American operation were somehow based on authentically valid considerations of national self-defense and if it were limited meticulously to certain presumptively nuclear military targets in Iran. For certain, in law, a more compelling case for preemption could be made by the State of Israel, which is substantially more vulnerable to any forthcoming Iranian nuclear developments than is the United States.

Israel is half the size of an American lake (Lake Michigan) and could face sudden and complete annihilation from almost any still-considered Iranian nuclear attack.

A related and sometimes derivative danger to Israel is posed by terrorist group surrogates. If not kept from receiving nuclear weapons or fissile materials from Iran, such proxies could sometime inflict starkly grievous harms upon variegated Israeli targets. In principle, at least, such harms could be nuclear, including determined rocket attacks against the Israeli nuclear reactor at Dimona. This attack plan was already attempted by Hamas several years back, but without any success. (This is discussed by Professor Beres in his latest book, Surviving Amid Chaos: Israel’s Nuclear Strategy

In the future, at least in principle, a non-nuclear insurgent adversary such as Hamas or Hezbollah could still visit significant nuclear harms upon Israel. Of  course, even by definition, any nuclear harms would be significant.

Where does all of this leave US President Donald Trump? Among other things, any observable use of preemptive force against Iran would almost certainly initiate a wider regional cycle of attack and counter-attack, destabilizing the entire area and very calculably expanding Israel’s overall strategic vulnerabilities. The actual likelihood of such markedly unwelcome  consequences would likely increase in some rough proportion to US inflicted harms.

This suggests, inter alia, that if the president’s determined military objectives were designed to halt Iranian nuclearization, these American efforts could have some limited success but only at a much greater overall strategic cost. As for any capable legal assessments, it is almost certain on its face that a preemptive strike against Iranian targets ordered by Donald Trump – even if exclusively military or hard-target oriented – would represent a prima facie act of US aggression.

It follows that Mr. Trump should now be looking in other operational directions and be seeking for altogether different remedies. As an overarching predictive concern, the president ought to be reminded that he is dealing here with unprecedented decisional circumstances, and that no logically reliable judgments could ever be made about prospects that are literally sui generis. Indeed, in meaningfully scientific terms, no useful probability estimations could be made about preemptive attack outcomes before the actual occurrence of a two-party nuclear war.

Best that we should all remain unable to offer any such estimations.


Louis Rene Beres (Ph.D., Princeton, 1971) is the author of many books and articles dealing with nuclear weapons and world politics. In Israel, he was Chair of Project Daniel (2003). Professor Beres’ most recent scholarly writings can be found at JURIST and in Israel Defense; The Harvard National Security Journal (Harvard Law School); The International Journal of Intelligence and Counterintelligence; The Brown Journal of World Affairs; Yale Global Online; Parameters: Journal of the U.S. Army War College; The War Room (Pentagon); Modern War Institute (West Point); The Hill; The National Interest; The Israel Journal of Foreign Affairs; The Jerusalem Post; and Oxford University Press. Dr. Beres was born in Zürich, Switzerland, at the end of World War II. His twelfth and latest book is Surviving Amid Chaos: Israel’s Nuclear Strategy, Rowman & Littlefield, 2016 (2nd ed., 2018)


Suggested citation: Louis René Beres, America, Iran, and “Anticipatory Self-Defense”: International Legal Standards of Presidential War-Making Decision, JURIST – Academic Commentary, July 5,2019,



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