Of Evolving Belligerent Occupation Law: Old “Hague” Occupation and New “Geneva” Occupation

For years, the legal status of so-called “functional occupation” was unclear in international humanitarian law (IHL) (see, e.g., this 2012 work by Zwanenburg, Bothe, and Sassòli). In 2024, however, the International Court of Justice (ICJ) adopted a new take on occupation, paving the way for a new alternative and a reshuffling of the law.

In its advisory opinion, Legal Consequences arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, including East Jerusalem (2024), the Court observed,

The foregoing analysis indicates that, for the purpose of determining whether a territory remains occupied under international law, the decisive criterion is not whether the occupying Power retains its physical military presence in the territory at all times but rather whether its authority “has been established and can be exercised” (Article 42 of the Regulations Respecting the Laws and Customs of War on Land annexed to the Fourth Hague Convention of 18 October 1907; hereinafter the “Hague Regulations”). Where an occupying Power, having previously established its authority in the occupied territory, later withdraws its physical presence in part or in whole, it may still bear obligations under the law of occupation to the extent that it remains capable of exercising, and continues to exercise, elements of its authority in place of the local government (para. 92) (parenthetical citation included in original).

A subsequent ICJ advisory opinion, Obligations of Israel in relation to the Presence and Activities of the United Nations, Other International Organizations and Third States in and in relation to the Occupied Palestinian Territory (2025), confirmed this stance, with the Court indicating,

The Court recalls that it found in the Advisory Opinion on the Legal Consequences arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, including East Jerusalem that, after the withdrawal of its military presence in 2005, “Israel remained capable of exercising, and continued to exercise, certain key elements of authority over the Gaza Strip”, and that Israel’s obligations under the law of occupation “have remained commensurate with the degree of its effective control over the Gaza Strip” (Advisory Opinion of 19 July 2024, paras. 93–94). These findings were based on the control exercised by Israel over the Gaza Strip prior to 7 October 2023, including control of the land, sea and air borders, restrictions on movement of people and goods, collection of import and export taxes, and military control over the buffer zone … (para. 85).

In effect, this jurisprudence created two distinct approaches in the law of belligerent occupation.

Classical Hague Occupation

According to Article 42 of the 1899/1907 Hague Regulations (hereinafter, “Hague Occupation”), classical requirements, which are cumulative and strict, govern occupation. According to Article 42(1) of the Hague Regulations, “Territory is considered to be occupied when it is actually placed under the authority of the hostile army.” The next section of Article 42 makes even clearer the principle of effective control, speaking to the capacity to exercise the power. Article 42 of the Hague Regulations imposes various criteria—some positive, some negative—for determining whether a belligerent occupation exists.

First, the occupation must be hostile, meaning that it is not based on consent given to the foreign military presence by the territorial sovereign. Second, occupation must be an incident of warfare, which thus rests on the advancing of one army and the retreat of the other, with the advancing military forces ultimately taking control of the territory. On this point, occupation is a military fact. Third, such military forces must be present on the territory (effectiveness). As with blockades, there are no “paper occupations.” The presence must be one of territorial control, meaning all hostilities, including all major movement and fighting, must have ceased to a significant extent (some pockets of resistance can remain to the extent they do not challenge the control of the foreign army). Moreover, this territorial control must have been transferred into the armed forces (or other force under the control of the armed forces) or an incoming administration of the occupied territory.

On the negative side, practice has settled the point that administration of territory under UN mandates does not trigger the law of belligerent occupation but remains governed by the law of the applicable UN Security Council resolutions (particular, not general, international law). To the extent that doing so is appropriate, this does not exclude applying by analogy some rules of the law of belligerent occupation.

If these stringent Hague Occupation conditions are met, the entire body of occupation law applies. This is because certain duties of the occupying power presuppose a physical presence, notably its primary duty to maintain public order and to provide for the needs of civilian life (keeping records, etc.), as stipulated in Article 43 of the Hague Regulations. Occupying powers cannot perform these duties remotely.

In short, this type of classical occupation is based on effective control by physical presence and is opposed to “paper occupation” by mere proclamation. It is also “plenary,” meaning that all provisions of the law of belligerent occupation apply. It furthermore supposes that hostilities do not flare up again to a significant degree. Finally, this type of occupation ensures a high degree of legal certainty, in the sense that it is clear from the beginning that all relevant provisions will apply lock, stock, and barrel.

Newer Geneva Occupation

Aside from Hague Occupation, there is the newer law of occupation according to the Fourth Geneva Convention of 1949 (GC IV) (hereinafter, “Geneva Occupation”), which prioritizes humanitarian obligations. Geneva Occupation, as developed in the last several decades, does not presuppose a firmly established presence in the occupied territory. It applies instead in a variable, fractional, and fragmented manner, each case depending on the activities over which the foreign power exercises effective control. This type of fragmented occupation may occur at the beginning of the conflict or at later phases.

Thus, for the invasion phase, certain humanitarian obligations, such as the prohibition of deportation or forcible transfer under Article 49 of GC IV, may apply upon the invasion of a territory—not just when the territory is formally occupied—even though the relevant provision falls under the part of GC IV concerning occupied territories. In this case, the invading army’s control over the territory suffices to impose negative obligations (“not to do”) that are purely humanitarian in nature.

Separate from the protections afforded individuals in Article 27 of GC IV, it would be preposterous to suggest that invading forces could deport civilians in the invasion phase to avoid incurring additional legal responsibilities if they gained firmer control over the territory and happened to become its occupier. Similarly, at a later stage, if an occupying power withdraws from a territory but retains control over the borders and thereby effectively controls certain activities (e.g., the transit of humanitarian aid and other types of necessary supplies), but not the territory, the occupying power will incur the obligations of the occupier linked to its control. This is the case when, and only when, the concrete activity under consideration is precisely under the occupying power’s control.

Geneva Occupation law is thus fragmented, relying on a mixed rationale of humanitarian protections (this being the aim of IHL) and effectiveness of control (reduced here to “activities” rather than “territory”). Geneva Occupation is “non-plenary,” meaning only some provisions of the law of belligerent occupation apply, depending on shifting degrees of control and types of activities (e.g., when an armed force controls a border). Geneva Occupation also does not require the cessation of major hostilities, but applies in parallel to the conduct of hostilities (hence the ICJ’s 2025 advisory opinion at para. 87). Finally, Geneva Occupation does not lend itself to a particularly high degree of legal certainty, as it may be less clear which provisions of the law apply and to what extent, given the analysis’s close connection to shifting degrees of fragmented control.

Conclusion

The ICJ’s recent jurisprudence has ushered in a new dual régime of occupation: Hague Occupation, for “on-the-spot” control; and Geneva Occupation, for “activities” control. Each one of these limbs complements the other. Compared to Hague Law alone, this dual régime has considerably diminished the minimum conditions necessary for a belligerent to incur occupier responsibilities.

Scholars and practitioners must read this evolution in the law in the context of ensuring better humanitarian protection of civilian populations in situations such as Gaza. The gist of the matter is that “boots on the ground” are no longer required for a military action to trigger the law of occupation. All other forms of effective control over occupation-like activities also trigger occupation law, at least in part. Taking the condition of effective control seriously, as well as the link between activities and duties under occupation law, can preserve legal certainty and minimize the risk of arbitrary cherry-picking of applicable legal provisions.

In effect, the ICJ has adopted a new form of occupation law. This opens new perspectives for the so-called “functional occupation” theory, which continues its ascent, notwithstanding its lack of endorsement in black-letter law and recent scholarship.

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Robert Kolb is a Professor of Public International Law at the University of Geneva and former legal staff member of the ICRC. Prof Kolb is also a member of the legal section of the Swiss military high command (IHL section).

The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.

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Photo credit: Israeli Defence Forces Spokesperson’s Unit