On Tuesday, the situation in the Caribbean escalated dramatically, with President Donald Trump announcing on Truth Social that he was “ordering A TOTAL AND COMPLETE BLOCKADE OF ALL SANCTIONED OIL TANKERS going into, and out of, Venezuela.” Citing the size of the force assembled in the area, Trump warned, “It will only get bigger, and the shock to [Venezuela] will be like nothing they have ever seen before — Until such time as they return to the United States of America all of the Oil, Land, and other Assets that they previously stole from us.” Claiming “[t]he illegitimate Maduro Regime is using Oil from these stolen Oil Fields to finance themselves, Drug Terrorism, Human Trafficking, Murder, and Kidnapping,” Trump closed by proclaiming, “America will not allow Criminals, Terrorists, or other Countries, to rob, threaten, or harm our Nation and, likewise, will not allow a Hostile Regime to take our Oil, Land, or any other Assets, all of which must be returned to the United States, IMMEDIATELY.” The Washington Post reported the following day that “[o]ne person familiar with the situation … said to expect more forceful U.S. naval operations in the next several days.”
While Trump accurately characterizes the Maduro regime as illegitimate, having failed to turn over power after losing the July 2024 elections, the claims about Venezuela being a major source of drugs coming into the United States fall apart upon examination. But one can even assume for the sake of analysis that the claims are correct, because they would not change the international law analysis.
In this article, we examine the Trump administration’s announced blockade from an international law perspective. There are basically two questions. First, would mounting such a blockade violate the prohibition on the threat or use of force under Article 2(4) of the UN Charter and customary international law? And second, would doing so initiate an international armed conflict between the United States and Venezuela, triggering the applicable law of armed conflict?
Before turning to these issues, it is first necessary to distinguish the operation Trump is threatening from blockades during armed conflict governed by the law of naval warfare, for which there is well-developed law containing granular requirements. Under the law of naval warfare, “[a] blockade is an operation by a belligerent State to prevent vessels and/or aircraft of all States, enemy as well as neutral, from entering or exiting specified ports, airfields, or coastal areas belonging to, occupied by, or under the control of an enemy belligerent State” (DoD Law of War Manual, § 13.10; see also Newport Manual on the Law of Naval Warfare, Drew, Heintschel von Heinegg).
We are not there yet because, so far, there is no international armed conflict with Venezuela. And the nature of the proposed interference with shipping would not qualify as a naval warfare blockade. Therefore, in the first part of this article, the term “blockade” is used to denote the threat or use of armed force to prevent specified vessels from entering or leaving the territorial waters of Venezuela. But as will become clear, status as a blockade meeting the requirements for such under the law of naval warfare does bear on whether the situation qualifies as an armed conflict. It is this form of blockade that we examine in the second part of the article.
Finally, we do not deal with the international criminal law implications of the action. However, it merits mention that the International Criminal Court Statute includes blockade (art. 8 bis (2)(c)) as a form of the crime of aggression. In our view, the offense is also of a customary character, and some States take the position that the crime of aggression is subject to universal jurisdiction. Of course, any attempt to prosecute U.S. officials who decided to implement the operations would face significant legal, practical, and political hurdles. The particularities of the ICC Statute on the crime of aggression preclude application to the United States.
Blockade as a Threat or Use of Force?
Article 2(4) of the UN Charter, which reflects customary international law, provides, “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the Purposes of the United Nations.”
Before turning to the question of whether a blockade qualifies as a use of force, readers are reminded that U.S. operations already violate the prohibition on threatening force, a topic examined in detail in a previous Just Security article. As explained there, the threat must be communicated, coercive, credible, and threaten unlawful force, criteria that have already been satisfied by the administration’s statements and the nature of the U.S. military deployment into the area. The Truth Social post threat to use force against Venezuela if Maduro does not capitulate further strengthens characterization of the U.S. operations in the region as a threat in violation of Article 2(4) and customary law.
Whether the threat of a blockade, as distinct from threatened operations into Venezuela, violates the prohibition on threats depends on the lawfulness of the threatened blockade. And, once the United States implements the blockade, which it presumably will do imminently, the question becomes whether it amounts to an unlawful use of force.
As a matter of law, peacetime “blockades” qualify as a use of force even before force is used against ships attempting to breach them. This characterization is relatively well-settled in international law. For instance, Article 42 of the UN Charter allows the UN Security Council to authorize “action by air, sea, or land forces as may be necessary to maintain or restore international peace and security.” It may do so after determining that “measures not involving the use of armed force” under Article 41 “would be inadequate or have proved to be inadequate.” Article 42 cites “blockade” as an example of an operation the Security Council can authorize when non-forceful measures have failed or are likely to prove ineffective. Although not every measure authorized under Article 42 need qualify as a use of force, the fact that the article cites blockade in contrast to non-forceful measures referenced in Article 41 supports such a characterization.
Even more telling is the U.N. General Assembly’s Definition of Aggression Resolution (UNGA 3314), adopted by consensus in 1974 without objection from the United States. The resolution was adopted in part to clarify Article 39 of the UN Charter, which is the trigger for action under Chapter VII, in particular Articles 41 and 42. Aggression is one of the situations cited in Article 39 as activating those articles; the others are a “threat to the peace” and a “breach of the peace.”
Article 1 of the resolution provides, “Aggression is the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State, or in any other manner inconsistent with the Charter of the United Nations.” The article’s verbatim inclusion of the language from the UN Charter’s prohibition on the use of force confirms that all acts of aggression constitute uses of force. Indeed, the preamble to the resolution states that “aggression is the most serious and dangerous form of the illegal use of force.”
So, it is clear that if an act constitutes aggression, it necessarily involves the use of force. Usefully, Article 3 of the Resolution provides a list of non-exhaustive acts that “qualify as an act of aggression. Among them is “[t]he blockade of the ports or coasts of a State by the armed forces of another State” (art. 3(c)). Thus, not only is a blockade a use of force, but it is also a specifically particularized — indeed, “most serious and dangerous” – form of it.
Eminent scholars are in accord. Ian Brownlie, in his classic 1963 work, International Law and the Use of Force by States, observed that “a naval blockade involves an unlawful use of force, although the tactical posture is passive, since its actual enforcement includes the use of force against vessels of the coastal state”(pages 365-66). The same year, in a famous American Journal of International Law article, Quincy Wright dismissed the argument that the so-called maritime “quarantine” of Cuba the United States established in response to the installation of Soviet nuclear missiles on the island could qualify as a “pacific blockade,” a term referring to the 19th century practice of a blockade imposed outside a state of war and directed solely at the target State’s vessels. As Wright noted, the U.N. Charter had extinguished any right under international law to impose such a blockade. He concluded, “It cannot be easily argued … that the United States has lived up to its legal obligations to respect the freedom of the seas, to submit threats to the peace to the United Nations before taking unilateral action, and to refrain from use or threat of force in international relations.” And in his masterwork, War, Aggression and Self-Defence, Yoram Dinstein rejected the premise that the quarantine was a lawful exercise of self-defense. This is significant because the U.S. partial blockade of Cuba would need to qualify as an act of self-defense only if it first amounted to a use of force. In other words, and simply put, the so-called Cuban missile crisis quarantine was an unlawful use of force.
The question, therefore, is whether a demand for the return of unspecified land, oil, and assets, combined with a vast military operation designed to control access to and from Venezuela’s territorial waters by force, if necessary, qualifies as aggression. In our opinion, it clearly does, particularly in light of Article 5(1) of the Definition of Aggression, which emphasizes that “[n]o consideration of whatever nature, whether political, economic, military or otherwise, may serve as a justification for aggression.”
We do note that the Truth Social post seems to hint at self-defense as the basis for the action, although not explicitly. The applicability of UN Charter Article 51 to national self-defense has been very ably addressed elsewhere (see, esp., articles in the Just Security collection). The near-unanimous view is that the United States does not enjoy the right of self-defense in the face of the drug threat on either the facts or the law (but see Kraska and Pedrozo). Now, President Trump has gone even further, leveling impossibly vague claims about oil, land, and “other assets.” In our view, those claims only serve to further weaken the administration’s case by detracting from the seriousness of the original assertions.
Not only is a blockade a use of force, but it is also a specifically particularized — indeed, “most serious and dangerous” – form of it.
Importantly, if a blockade is a use of force, it is also an “armed attack” triggering the right of self-defense on the part of the blockaded State by the United States’ own interpretation of the right of self-defense (DoD, Law of War Manual, §1.11.5.2). Most States, however, are of the view that an armed attack is the “most grave” form of the use of force (Paramilitary Activities, ¶ 191). Yet, recall that the Definition of Aggression resolution characterizes aggression as the “most serious and dangerous form” of the use of force. What’s more, the operation described by President Trump involves a scale and gravity that meets the threshold for an “armed attack” articulated by the International Court of Justice. Thus, even under the more restrictive view adopted by these States and international bodies, the U.S. action, if implemented, would be clearly illegal and trigger Venezuela’s right to use force in self-defense.
Blockade Triggering International Armed Conflict?
The second issue is whether the imposition of a blockade by the United States would trigger an armed conflict between the United States and Venezuela (Geneva Conventions, Common art. 2) . It would in two circumstances. The first would be if United States forces board and take control (or otherwise forcibly interfere with the transit) of a Venezuelan-flagged tanker, or indeed any other Venezuelan vessel.
The International Criminal Tribunal for the former Yugoslavia articulated the well-accepted standard for the existence of an international armed conflict in its Tadić decision (Jurisdiction, ¶ 70). There, the Tribunal observed that an international armed conflict exists “whenever there is a resort to armed force between States.” This is a position accepted by the United States. As the DoD Law of War Manual explains, “The United States has interpreted ‘armed conflict’ in Common Article 2 of the 1949 Geneva Conventions to include ‘any situation in which there is hostile action between the armed forces of two parties, regardless of the duration, intensity or scope of the fighting.’” Non-consensually taking control by military means of a Venezuelan-flagged vessel, given the threats made by administration officials against Venezuela, would clearly satisfy this standard, as it would involve the use of military force by one State against another.
As a side note, we caution that a seized vessel’s status under U.S. sanctions is of no significance under international law, unless it is Stateless and on the high seas or those sanctions are the domestic implementation of Chapter VII sanctions authorized by the UN Security Council (see our analysis here and here). In other words, any claim to be enforcing U.S. law would not affect classification as an international armed conflict.
The second possibility is that the very establishment of the blockade, standing alone, would trigger an international armed conflict. This, in our view, depends on whether the operation described by President Trump qualifies as a “blockade” under the law of naval warfare, the applicable legal regime for maritime operations during an armed conflict. In other words, since the premise that a blockade triggers an armed conflict is found in the law of armed conflict, we must look to its definition as a legal term of art in that body of law.
Under the law of naval warfare, the declaration of such a blockade has traditionally been a threshold that, when crossed, brings into being an armed conflict between the States concerned. Famously, although in the context of the American Civil War, the U.S. Supreme Court, in its 1862 Prize Cases opinion, held that “[t]he Proclamation of blockade by the President is, of itself, conclusive evidence that a state of war existed.”
Some members of Congress have already concluded that the action is “unquestionably an act of war.” However, to be so for the purposes of triggering the law of armed conflict (the law that applies during armed hostilities, such as the Geneva Conventions), the criteria for a blockade set forth in the law of naval warfare would have to be satisfied. Those criteria are evident in both customary law and in certain instruments central to that body of law, such as the 1909 London Declaration. There are four.
The first requirement is notification, such as through Notices to Mariners (NTM) and Notices to Airmen (NOTAM). That notification must include details as to geographic extent, date of commencement, and general scope of measures employed (see, e.g., London Declaration, arts. 8-11). Post-WWII examples of blockade declarations are rare, but a few are publicly available and give some sense of the details required. These include the Iranian proclamation in Notice to Mariners No. 17/59 (Sept. 22, 1980) during the Iran-Iraq conflict (for text, see Guttry and Ronzitti), as amplified in several subsequent NTMs, and the contentious 2009 maritime blockade declaration issued by Israel in relation to Gaza.
In the current case, however, we are aware of no notification of sufficient detail to meet this fundamental requirement. In particular, as of the time of writing, there does not appear to have been a NAVAREA IV warning or special announcement regarding this blockade declaration, nor a Notice to Mariners. This could change in short order if and when the relevant warning or Notice to Mariners is promulgated, or some other notification pathway (e.g., to the UN Secretary-General) is employed.
The second requirement is that the blockade must be effective, meaning that sufficient military assets must be deployed to implement it. The 1856 Paris Declaration requires that “Blockades, in order to be binding, must be effective, that is to say, maintained by a force sufficient really to prevent access to the coast of the enemy.” Article 3 of the London Declaration adds that this is “a question of fact.”
There are questions surrounding the scope of this requirement, such as the validity of the concept of “distant blockade,” the paradigmatic example being the British blockade of German ports in WW I, when the main Battlefleet was located in Scapa Flow rather than on continuous station off the German coast. In the current case, however, the concentration of forces off the coast of Venezuela would clearly meet the “force capable of enforcing the blockade” requirement.
However, here the blockade apparently involves only sanctioned vessels carrying oil. Blockade is traditionally required to cover all imports and exports, so long as it does not prevent certain cargoes from passing through – chiefly humanitarian items (see below). So, even though a force readily able to effectively enforce the blockade is on-station, the effectiveness requirement has not been met.
If an armed conflict was already underway, the appropriate method for addressing individual items would be to declare them “contraband,” that is, “goods which are ultimately destined for territory under the control of the enemy and which may be susceptible for use in armed conflict” (San Remo Manual, rule 148). But even that would not work here because a visit and search regime to enforce a contraband list concerns items being transported into the adversary’s ports, not leaving them. And, in any event, seizures of Venezuelan oil exports from “neutral” tankers during an armed conflict would still involve Prize Law jurisdiction (see below).
The third requirement is impartiality (London Declaration, art. 5), which requires that the “blockade … be enforced against all vessels (and/or aircraft), regardless of flag or status as a State or private vessel or aircraft” (Newport Manual, ¶ 7.4.4). In this case, however, the blockade specifically targets “all sanctioned oil tankers going into, and out of, Venezuela.” Thus, it is not impartial because it is focused only on one type of vessel – oil tankers – and only on those that have been sanctioned. Indeed, Reuters has reported that as of last week, “30 of the 80 ships in Venezuelan waters or approaching the country were under U.S. sanctions.” Since fewer than half are subject to the blockade, the impartiality requirement is not satisfied.
The final requirement is that the blockade must comply with certain humanitarian concerns. In particular, the operation is “prohibited if it is solely intended to starve the civilian population, or solely intended to deprive the civilian population of objects essential to its survival” (Newport Manual, ¶ 7.4.5). Given the narrow focus of the blockade – oil – this is the only blockade requirement satisfied.
Consequently, based on the information currently at hand, there is no valid law of naval warfare blockade in place. This leaves the first ground, using armed force to take control or otherwise impede transit of Venezuelan vessels, as the sole basis to link the blockade to initiation of an international armed conflict. That said, if the United States tightens the blockade to comply with the remaining three criteria, it will have initiated an international armed conflict even before any vessels had been boarded.
If that were to happen, the United States would need to ensure its courts are ready to apply prize law, given that capture of a vessel for breach of a (valid) law of naval warfare blockade is not the same as condemnation into the ownership of the capturing State without compensation. Prize Law generally requires that in the case of a captured blockade runner, final condemnation – i.e., ownership of the vessel and the cargo passing to the capturing State – requires an independent Prize Court decision (Newport Manual, ¶¶ 9.1 and 9. 14).
Finally, the United States is taking the blockade action against Venezuela. But if there were an ongoing non-international armed conflict with one or more of the cartels, which there is not (despite the administration’s claims, see the multiple pieces explaining why in the Just Security collection), and the blockade was directed at them and satisfied the four criteria, this would constitute tacit recognition of that non-State actor’s belligerency. The consequence of that recognition would be that operations against the cartels would have to be conducted in accordance with the law applicable in international armed conflict, including its rules on detention and the conduct of hostilities.
Concluding Thoughts
President Trump’s threat to impose a maritime blockade on specified vessels entering or leaving the Venezuelan territorial sea is a clear violation of the prohibition on the threat of the use of force under Article 2(4) of the UN Charter and customary international law. If the announced blockade is implemented, it will qualify as an unlawful use of force, not merely a threatened one. Execution of the blockade would constitute an act of aggression, which by definition is an unlawful use of force. It would also qualify as an armed attack by the United States on Venezuela, thereby triggering Venezuela’s right to forcibly defend itself under Article 51 of the UN Charter and customary international law.
Only if the United States expands its blockade in a manner that satisfies the law of naval warfare blockade criteria will the declaration of the blockade, standing alone, initiate an armed conflict. That said, if U.S. forces engage with or seize control of Venezuelan-flagged vessels, the United States will have initiated an international armed conflict, triggering applicability of the law of armed conflict in any hostilities between the United States and Venezuela. And we hasten to add that, as explained in numerous Just Security posts, even if an international armed conflict did commence, U.S. operations against the boats alleged to be transporting drugs would continue to be governed by international human rights law, not the law of armed conflict.
FEATURED IMAGE: Two crude oil tankers remain anchored on Lake Maracaibo, near Maracaibo, Zulia state, Venezuela on December 17, 2025. (Photo by Alejandro Paredes / AFP via Getty Images)
Great Job Michael Schmitt & the Team @ Just Security Source link for sharing this story.
