Jakob Fletcher
The Trump administration has defended the current Iran operations as necessary to address an imminent nuclear and military threat.[1] Operation Epic Fury, so christened by the White House, has emphasized strikes on Iranian missile sites, drone sites, naval assets, and related capabilities.[2] The executive branch has justified these actions as defensive.[3] That label goes beyond political rhetoric. The constitutional allocation of war powers has long turned, at least in part, on whether a use of force is offensive or defensive[4]—a distinction the Framers inherited from the eighteenth-century law of nations. Whatever the precise contours of modern war powers doctrine might be,[5] understanding how that tradition drew the line is a natural place to start.
What counted as “defensive” war under the eighteenth-century law of nations? Emer de Vattel’s Law of Nations[6]—broadly regarded as highly probative of founding-era thought[7]—suggests a more complicated answer than modern orthodoxy might imply.
Vattel distinguishes war as “either defensive or offensive”[8] and places “defensive” between two outer bounds. It is narrower than “just,” because some offensive wars may be just. A war may be just because it vindicates a nation’s rights yet still count as offensive rather than defensive.[9] Even if the Iran operations were prudent, justified, or aimed at safety, that would not automatically make them defensive in the Vattelian sense. And truly offensive war—affirmatively seeking redress or vindication of rights—carried the ordinary expectation of declaration under the law of nations.[10]
But neither would the absence of an immediately preceding first blow automatically make them offensive.[11] “Defensive” is a broader category than mere response to immediate attack. Nations may use force when necessary for their defense and for the preservation of their rights.[12] Vattel’s discussion of dangerous, aggrandizing neighbors clarifies that states need not wait helplessly for a threat to materialize into overt action.[13] The relevant historical framework, therefore, is more demanding than broad appeals to justice but less cramped than a first-shot test.
Viewed through Vattel, the Iran operations are not usefully analyzed by asking only whether they were broadly justified or whether they repelled an immediate attack. The more precise questions are whether the United States was responding to unjust aggression, whether the claimed threat had matured enough to count as a present danger rather than a speculative future risk, whether the object of force was protection rather than conquest or punishment, and what role prior demands, satisfaction, or requests for security play in the analysis. If the administration’s description of the campaign is taken on its own terms—as focused on Iranian missiles, drones, naval assets, and related capabilities rather than annexation or territorial gain[14]—those questions are at least more complicated than a purely reactive view of defense would suggest. Vattel’s framework does not eliminate the need for judgment, but it does suggest that a use of force may be defensive even when it is preventive in posture, so long as it is directed at repelling or disabling a grave threat rather than affirmatively vindicating rights or seeking redress through aggression.
Whether the current Iran operations ultimately satisfy that standard is a further question—one that turns on contested facts and the full range of war powers doctrine well beyond Vattel’s framework alone. But on the narrower question of what counts as defensive war, Vattel and the eighteenth-century law of nations help clarify the inquiry.
[1] Peace Through Strength: President Trump Launches Operation Epic Fury to Crush Iranian Regime, End Nuclear Threat, The White House, https://www.whitehouse.gov/releases/2026/03/peace-through-strength-president-trump-launches-operation-epic-fury-to-crush-iranian-regime-end-nuclear-threat/ (last visited Mar. 29, 2026); The Iranian Regime’s Decades of Terrorism Against American Citizens, The White House, https://www.whitehouse.gov/releases/2026/03/the-iranian-regimes-decades-of-terrorism-against-american-citizens/ (last visited Mar. 29, 2026).
[2] Operation Epic Fury, U.S. Dep’t War, https://www.war.gov/Spotlights/Operation-Epic-Fury/ (last visited Mar. 29, 2026).
[3] Joint Statement on Iran’s Missile and Drone Attacks in the Region, U.S. Dep’t State, https://www.state.gov/releases/office-of-the-spokesperson/2026/03/joint-statement-on-irans-missile-and-drone-attacks-in-the-region/ (last visited Mar. 29, 2026).
[4] For discussion on the difference in executive power in offensive vs. defensive actions in regard to, inter alia, Jefferson’s opposition to Barbary pirates in Tripoli and Polk’s deployment of troops to the Mexico border, see, e.g., J. Gregory Sidak, To Declare War, 41 Duke L.J. 27 (1991) and Michael D. Ramsey, Textualism and War Powers, 69 U. Chi. L. Rev. 1543 (2002).
[5] See generally Cong. Rsch. Serv., “Make War” and “Declare War” at the Constitutional Convention, Const. Annotated, https://constitution.congress.gov/browse/essay/artI-S8-C11-2-2-3/ALDE_00013911/ (last visited Mar. 29, 2026) (noting the Convention’s effort to preserve presidential power to repel attacks); Presidential Power to Use the Armed Forces Abroad Without Statutory Authorization, 40 Op. O.L.C. 185 (1980) (providing the controversial basis for the modern presidential assertion of broad power to engage in limited-scope foreign conflicts without a declaration of war).
[6] Emer de Vattel, The Law of Nations, or, Principles of the Law of Nature, Applied to the Conduct and Affairs of Nations and Sovereigns, with Three Early Essays on the Origin and Nature of Natural Law and on Luxury (Béla Kapossy & Richard Whatmore eds., Thomas Nugent Trans., Liberty Fund 2008) (London Edition 1797) [hereinafter Vattel, The Law of Nations] (French original published in 1758).
[7]See, e.g., Vincent Chetail, Vattel and the American Dream: An Inquiry into the Reception of The Law Of Nations in The United States in The Roots of International Law at 254 (Pierre-Marie Dupuy & Vincent Chetail eds., 2014) (“No other treatise on international law has been more widely read and cited than The Law of Nations by Vattel”). But see Brian Richardson, The Use of Vattel in the American Law of Nations, 106 Am. J. Int’l L. 547 (2012) (challenging the merits of Vattel’s predominance as a standalone source for founding-era international law understanding).
[8] Vattel, The Law of Nations, supra note 6, at 307.
[9] Id. at 315–16.
[10] A declaration is, for Vattel, a final appeal to justice before open war; but where the use of force is properly classified as defensive, no such declaration is required. And even in the case of offensive war, the law of nations does not require a declaration for the purpose of giving the enemy time to prepare. Id. at 328–33.
[11] Id. at 322.
[12] Id.
[13] Vattel carefully wrestles with the question of a dangerous aggrandizing neighbor. Gaining power alone is insufficient to justify preemptive defense, but where a state has already demonstrated hostile will and other satisfaction has been refused, grave danger may justify defensive action before the threat fully materializes. Id. at 321–24.
[14] Operation Epic Fury, supra note 2.