Who Are the Houthis?

Over the past decade, the Gulf of Aden has become the epicentre of a complex and multifaceted conflict characterised, among other things, by the presence and conduct of a private group named Houthis. Since 2015, Houthis have engaged in a civil war against the Yemeni government and, at the same time, have undertaken a set of piratical attacks against ships of various nationalities. This conflict, which initially assumed the shape of a “proxy war” against Israel and Saudi Arabia in the context of the Gaza war, is now part and parcel of the wider Hormuz and Bab el-Mandeb crisis, but its precise boundaries and shape are very hard to define. Some authors suggested framing the scenario in the Red Sea as the sum of several intertwined conflicts – a civil war taking place in Yemen and separate conflicts involving other States. A partially different interpretation frames the conflict in Yemen as split into two: the initial coup d’état tentatively put on hold in 2022 by a ceasefire and new conflicts between Houthis and other States.

Be that as it may, the Houthis and their relationship with other concerned States in the area play a leading role in what may be currently defined as a regional armed conflict, where the private component represents a pivotal aspect and has a direct and deep impact on, inter alia, oil supplies at the global level. The aim of this post is therefore to sketch a reflection on the challenges posed by this group to the law of international responsibility. Such reflection may, in turn, serve as a starting point to expand the discourse to further implications of the role of non-State actors, such as the intrinsic imbalances in the way international law apprehends these phenomena.

The Houthis and General International Law: Insurgents or Pirates?

At first sight, Houthis may be defined as “simple” insurgents, given their clear opposition to the official Yemeni government. However, the complexity of the current political landscape within this State and, notably, its uncertain power structure prevent a straightforward definition under this legal category. Regarding the scenario at stake here, it would be bold to argue that Houthis’ attacks are by definition linked to the civil war taking place in Yemen, especially since 7 October 2023, when their “proxy war” against Israel began. At the same time, such “proxy war”, and the related political aims, are not always clearly identifiable, also in light of its intertwining with the Straits crisis.

On a wider level, these elements bring to the fore the long-debated issue of the interpretation of the “private end” requirement mentioned by Article 101 UNCLOS as a component of piracy. Under the terms of this latter provision, maritime piracy is deemed to exist when an illegal act of violence is committed on the high seas by a ship against another ship in the pursuit of “private ends”. On the one hand, it is nowadays uncontroversial that animus furandi is not necessary and that “simple” acts of violence and depredation are sufficient for this purpose. On the other hand, the surge of maritime terrorism that took place at the end of the last century warned about a possible abuse of allegedly “public aims” and, not by chance, prompted the adoption of the 1988 Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation.

Such uncertainties are clearly reflected in the recent codification work on piracy and armed robbery at sea undertaken by both the International Law Commission and by the Institut de droit international, where the persistence of the “private ends requirement” coexists with the recognition that the notion may have a wide range of meanings, depending, inter alia, on the national legal order that needs to be taken into account. Additional insights come from the Special Rapporteur of the ILC who, while admitting the contact points between maritime terrorism and piracy, raises doubts as to the usefulness of this theme in the light of the considerable differences between national legal systems, many of which do not even mention the purposes of piracy. A partially different view emerges from the Institut de droit international preparatory work, apparently based on a functional approach, i.e. avoiding any interpretation of this notion that could unduly justify “acts of violence at sea”. In line with these developments, some authors underline the possibility that private individuals may evade classification as pirates when they act on political or philosophical grounds, thus considering these hypotheses as providing a more faithful picture of the situation when compared to a simple assessment of whether the concerned individuals represent a State or not. It is finally important to highlight that at least some attacks by the Houthis might not satisfy the “two-ships requirement” set by Art. 101 UNCLOS. This is notably the case with attacks carried out through drone boats and aerial drones: The reference in Article 101(a) to crew and passengers seems to exclude unmanned vehicles from its scope, whereas drones would definitely not fit the definition laid down in this provision, which is based on the notion of “ship”.

The Houthis as a Non-International Armed Group (NIAG) Under International Humanitarian Law

Given the Houthis’ involvement in armed conflicts, their potential role under the relevant categories of international humanitarian law (IHL) definitely deserves attention. Assuming that the conflict with the Yemeni government could hardly be considered as having been undertaken in pursuance of the principle of self-determination under Article 1(4) of the 1977 Additional Protocol I to the Geneva Conventions, the Houthis could qualify as a NIAG. Therefore, their conduct may be regulated by common Article 3 of the Geneva Conventions and by the 1977 Additional Protocol II, whose Article 1(1) “develops and supplements” this last provision. As is well known, Article 3 binds “each Party” to a non-international armed conflict taking place in the territory of a Contracting Party to respect a noyau dur of legal obligations. In this respect, it is interesting to take note of the creation, since 2024, of a Houthis-run Humanitarian Operations Coordination Centre, precisely aimed at mitigating the humanitarian effects and repercussions of military operations through adherence to inter alia IHL.

Though of a certain weight, such an element is not sufficient in itself to ground the application of Article 3 to Houthis. While the Geneva Conventions and their Protocols do not clearly define an armed conflict, relevant criteria to this end are to be found in the so-called “Tadic formula” – e.g., the existence of an organized structure, the threshold of the conflict, the control over a part of territory. As things currently stand, it could be argued that such a formula is, in many respects, fulfilled. The Houthis have reached a rather developed internal organization, exercise control over a part of territory and marine areas and are capable of large-scale attacks, as the ones recently carried out against Saudi Arabia airports and pipelines.

At the same time, Houthis’ role might be analysed by focussing on their capacity to incur international responsibility based on the scope of application of IHL. Notably, such a hypothesis may be grounded on common Article 1 of Geneva Conventions and, notably, on the due diligence obligation stemming from the duty to “ensure respect” for their provisions. Such “external dimension” of Article 1 would attribute both positive and negative obligations concerning the conduct of any person or entity, under the Parties’ jurisdiction, that is a party to a conflict and, as has been observed, would be fully justified in light of the humanitarian purpose of this corpus of international law. As linear as this reasoning may appear, its application to the case under analysis herein is not straightforward, if one considers that for Article 1 to deploy its “external dimension”, a sufficiently close relationship between the NIAG and a concerned State is necessary. It is precisely this aspect that might hinder the application of a due diligence obligation in this context, as it would currently be difficult to identify a State in the position to influence or even to direct Houthis’ conduct.

The Houthis as Private Actors Engaging State Responsibility

Widening the analysis from IHL to general international law and, more precisely, to the law of international responsibility, the question arises as to whether the relationship between the Houthis and other States could lead to the attribution of the Houthis’ conduct to one of them through one of the modalities set out by ARSIWA. In this respect, the most plausible option seems to be the attribution of the Houthis’ conduct to Iran on the basis that Iran directs or controls them, under the terms of Article 8 ARSIWA, by virtue of logistical, financial and military support. On the one hand, it is doubtful whether such support could satisfy the requirements normally set by the International Court of Justice for the purposes of attribution, notably the existence of an “effective control” over the group’s activities. On the other hand, some authors put such test into discussion based on the specific test of attribution applicable in the field of aggression, requiring a “substantial involvement” in the activity – a requirement that Iran would probably easily satisfy. Unlike Article 8, Article 11 ARSIWA does not seem to lead to the attribution of the Houthis’ conduct to Iran. Although reliable sources have reported that Iran requested the Houthis to intervene in Bab el-Mandeb Strait, this State has never officially endorsed the Houthis’ action. Hence, the Houthis’ conduct cannot be deemed to have been acknowledged and adopted by Iran as its own, in accordance with Article 11.

Even less likely is to conclude to the attribution of the Houthis’ conduct to Iran under Article 9 ARSIWA whose application, according to the ILC Commentary, requires inter alia that the conduct of a person or group of persons was carried out in the absence or default of the official authorities and that “the circumstances must have been such as to call for the exercise of those elements of authority”. A similar negative outcome would apply to Article 10 ARSIWA, which concerns the attribution of the conduct of an insurrectional movement which becomes the new Government of a State, considering that Houthis as an insurrectional movement have not succeeded in the creation of new State, together with the lack of any continuity between the movement and the eventual Government. As regards, finally, the possibility of responsibility arising through one of the forms of responsibility “in connection with the act of another State” (Articles 16-18 ARSIWA), the main obstacle relates to the fact that these articles concern the relationship between States, and, thus the relationship between Houthis and Iran falls beyond their scope.

Naval Operations Against the Houthis and the Puzzle of Self Defence

The Houthis’ actions have been followed by several naval operations, including the US-led operation Prosperity Guardian and the EU-led operation EUNAVFOR Aspides, whose legal basis is not always easy to detect. In particular, doubts may arise in relation to the argument– purported by the US Department of Defence as well as by some authors –that the Houthis’ attacks constitute a direct threat to commerce and maritime security and to “essential security interests”, potentially justifying a response based on self-defence. One of the more evident problematic features of these arguments lies in the lack of any authorization to this end in UN Security Council resolution 2722 (2024): nowhere does its text refer to the relevant provisions of the UN Charter, nor does it qualify conduct by the Houthis as a breach of peace or as an act of aggression. International peace and security are mentioned in relation to the stability and prosperity of the coastal States of the Red Sea, whose sovereignty and territorial integrity are reaffirmed a few lines below. Hence, it is these latter aspects – and not the attacks – that are the focus of a potential intervention based on Chapter VII. Concerning the hypothetical use of force as a form of collective self-defence, the language employed by resolution 2722 (2024) equally raises several doubts, which are further confirmed by the lack of any clear reference to article 51 of the UN Charter. Besides this, resort to collective action would be excluded in the light of the lack of any request on the part of States other than those leading the naval operations.

Moreover, relevant uncertainties arise with respect to the threshold of gravity that an attack must reach to trigger self-defence: notwithstanding their seriousness, attacks by the Houthis might not have reached the degree of gravity required for this purpose, i.e. that giving rise to an armed attack. In this respect, specific legal issues are raised by the argument based on the reference to the ‘fleets’ of another State in the definition of aggression under UN General Assembly Resolution 3314 (1974), as the generic nature of this term leaves open the question of whether an attack on a limited number of ships would suffice to satisfy this requirement. Nor could it be argued that the gravity of the attacks by the Houthis might be based on the cumulative effect of individual attacks on targeted ships: as has been underlined, such an assessment must be made with regard to each State whose flag the targeted vessel flies, taking into account that one single attack would not be sufficient. Furthermore, the status of ships that have been the object of attacks is not irrelevant for the purposes of the fulfilment of the notion of aggression, in light of the language employed by Article 3(d) of UNGA Resolution 3314 (1974), which clearly states that an aggression occurs in the event of an attack “by the armed forces of a State on the […] sea […] forces” of another State. While naval vessels undoubtedly fall within this category, the same does not necessarily apply to cargo ships, especially if they are the only ones that have been targeted. A further, unresolved issue concerns the availability of self-defence against non-State actors, an option which has been excluded by the ICJ in its Wall advisory opinion. This acknowledgment of the ICJ delimits substantively, at least from an international law perspective, the relevance of the US Administration’s decision to qualify Houthis as “special designated global terrorists” in 2021 and, after having overcome some humanitarian concerns, as “foreign terrorist organization” in 2024.

Some Tentative Conclusions

In the light of the analysis above, it becomes clear that, on the one hand, due to their multifaceted features and to the complexity of the scenario where they act, the Houthis escape or at least seriously challenge international law categories such as those of piracy and insurgency. Notably, while the definition of piracy is still limited to a very specific phenomenon and, particularly because of the restrictive notion of “private ends” and by the “two-ships requirement”, insurgency refers to a very precise specific situation in which a private group aspires to become a new State and succeeds in this respect. On the other hand, the identification and application of legal constructs and devices suitable to link private actors to public international law, even when present, give rise to challenges. This is particularly true in the context of the law of state responsibility that, by definition, does not address the conduct of non-State actors if not under residual categories and in connection with state conduct. At the same time, similar difficulties may arise under IHL norms, for two reasons: the requirements a group must satisfy in order to fall under the definition of NIAG according to the relevant provisions of the Geneva Conventions and the application of the due diligence standard, potentially linking the group to a State.

At the same time, such lacunae are definitely inconsistent with the legal consequences that private actors, including the Houthis, often endure by virtue of their conduct. This is the case with the multinational naval missions undertaken by some States, whose legal justification is debatable. Similarly, the Houthis, like any other non-state actor, may be – and have been, in 2015 – the target of sanctions by the Security Council, while having no standing whatsoever in the structure of the UN and with very limited forms of review available. Notwithstanding the apparent advantage in terms of impunity arising from the gaps mentioned above, these inconsistencies reflect inherent asymmetries within the international community, which, despite struggling to recognise the agency shown by non-State actors, subjects them to its power structures. The dramatic and decisive impact of the Houthis’ actions in the current Straits crisis highlights the pressing need to identify legal tools to acknowledge the role and influence of these non-State actors in contexts where international peace and security, but also the availability of essential global supplies are at stake.