Use of Force in Self-Defence to Recover Occupied Territory: When Is It Permissible?

In a recent piece on Just Security, Tom Ruys and Felipe Rodríguez Silvestre argue that a state whose territory is unlawfully occupied by another state does not have the right to use of force in self-defence to recover the occupied territory. The post considered the position in relation to the recent armed conflict in Nagorno-Karabakh between Azerbaijan and Armenia and suggested that even if it is accepted that the region belongs to Azerbaijan, and is unlawfully occupied by Armenia, Azerbaijan will have lost any rights it may have had to act in self-defence because the status quo has lasted for a quarter of a century. Yesterday, in a post on this blog addressing a range of international legal issues regarding the conflict in Nagorno-Karabkh, Bernhard Knoll-Tudor and Daniel Mueller agreed with the position taken by Ruys and Silvestre arguing that ‘continued occupation cannot be equated with “continued attack” permitting the recourse to self-defence in line with Article 51 [of the UN Charter].’

Ruys and Silvestre set themselves the following question: ‘When part of a state’s territory is occupied by another state for a prolonged duration, can the former state still invoke the right of self-defence to justify military operations aimed at recovering its land? Put differently, can unlawful occupation be regarded as a continuing armed attack permitting recourse to self-defence at any given point in time—possibly years after occupation commenced?’

We think that the question is wrongly put—or at least incomplete. The point here is not whether an unlawful occupation constitutes a continuing armed attack, but whether any occupation that is the direct consequence of an armed attack constitutes a continuing armed attack. We argue below that such an occupation resulting from an armed attack on another state is indeed a continuing armed attack and that the attacked state does not lose its right to self-defence simply because of passage of time.

Distinguishing Between Settling Territorial Disputes by Force and the Use of Force in Self-Defence

First of all, one needs to draw the distinction between a territorial dispute and a situation of armed attack and occupation of territory. 

As Ruys and Silvestre observe, and of course we agree, it is trite law that territorial disputes cannot be resolved by recourse to force. This principle, which is outlined in the Friendly Relations Declaration (UNGA Res 2625) follows from the requirement in Article 2(3) of the Charter requiring that international disputes be settled by peaceful means, which itself follows from the prohibition of the use of force in Article 2(4) of the Charter. However, distinct from this is a situation of an armed attack, to which the right to use force in self-defence applies. Indeed, it would not be coherent for a principle which derives from Article 2(4) of the Charter to prevent the application of Article 51 which after all constitutes an exception to the prohibition in Article 2(4). To be fair, the authors, at the very end of their piece, and after having put much weight of the inadmissibility of force for the resolution of territorial disputes, recognise that ‘defining where self-defence stops and the prohibition of settling territorial disputes by force kicks in remains an extremely difficult exercise’ (our emphasis), and we agree. Yet it is precisely this exercise that needs to be undertaken.

The distinction that needs to be drawn then is between an outstanding territorial dispute where no force has yet been used by any of the disputing parties, and a situation where one party creates (or escalates) a territorial dispute by invading and occupying territory held by another state. While no force can be used by either party in the former instance, the latter instance is clearly one where an armed attack has taken place, and the right of self-defence is triggered.

To put it differently, it is one thing to invoke alleged title to territory in order to justify the use of force against another state (impermissible), and quite another to respond to an armed attack of another state that has led to the occupation of territory you previously held (without having occupied it through resort to force). In the former instance we have an attempt to settle a territorial dispute by force (which is impermissible). In the latter, we have an instance of the use of force in self-defence, even though it may still be possible that the title to  territory continues to be in dispute, and such dispute has to be resolved by peaceful means since no use of force can lead to annexation or otherwise lawful title to territory.

Continuing Armed Attacks

Second, we need to now discuss when, if ever, the right of self-defence ceases where one state has used force resulting in the occupation of (part of) the territory previously controlled by another state. Ruys and Silvestre seem to argue that the right of self-defence ceases at some (unclear) point in time when a status quo is established, eg when the territory has been occupied and administered peacefully and there is a prolonged absence of fighting. They do not tell us where that point in time is, but they seem to imply that a quarter of a century is long enough.

Ruys and Silvestre do mention Article 3(a) of the UN General Assembly Resolution on the Definition of Aggression (UNGA Res 3314), which goes directly against their view. It provides that ‘military occupation resulting from an invasion or attack’ constitutes aggression (our emphasis, and see further above our point on what is the right question to ask). They get around this rather significant obstacle to their argument by attempting to cast into doubt the relevance of the UN General Assembly Definition of Aggression for the concept of an ‘armed attack’ under Article 51 of the UN Charter. However, as we have written, the International Court of Justice has practically equated the notion of ‘aggression’ with the notion of ‘armed attack’ by relying on the UNGA Res 3314 Definition of Aggression in order to determine whether a particular use of force constitutes an armed attack in numerous instances, including in the Nicaragua case (para 195) the Armed Activities case (para 146).

Indeed, the Definition of Aggression makes it clear that occupation that results from an invasion or attack is aggression and must be one of a continuing character. And given that an invasion or attack that leads to occupation is certainly an armed attack within the meaning of Article 51 UNC, we fail to see how it simply stops being one if one were to just wait long enough. It is significant that state practice accepts, as it seems Ruys and Silvestre do too, that if there is a short of space of time between the initiation of the use of force that results in occupation and a response in self-defence then the right of self-defence persists. One can think of the UK’s response to the invasion and occupation of the Falkland Islands. If the right of self-defence exists in such cases, it can only because there continued to be an armed attack up to the point when the right of self-defence was being exercised. If it were to be accepted that the armed attack consists only of the initial act of invasion, and also accepted that self-defence is lawful in the sort of cases described above, this would open up the possibility that self-defence can be exercised even after an armed attack has ceased. The only justification for accepting self-defence in these cases is because the armed attack continues. But if it continues, what is it that would make it cease?

Ruys and Silvestre also make the point that Article 51 UNC states that there is a right of self-defence ‘if an armed attack occurs’, and thus the concept must be limited to a specific point in time. In the first place, the use of the word ‘occurs’ does not linguistically confine the attack to a specific point in time. It only means that such an attack must have occurred and presumably must be occurring. It does not set out how long it must occur for. The Charter says ‘if’ an armed attack occurs, and not ‘when’ it does. If it occurs, presumably it can occur for a rather long time. So, the ‘textual’ argument does not seem either compelling or dispositive here. In any case, in practice, armed attacks can occur for a lengthy period. One need only think of a case where after state A invades state B, fighting goes on within the territory of state B for several years. After a while, the tide turns and state B gets the upper hand and pushes state A back on to its own territory. At this point state B is now acting in self-defence on the territory of state A. Does the fact that the initial attack by state A began years ago and that it has been under attack for several years mean that state B no longer has the right of self-defence? One can think of the situation between Germany and the Soviet Union in the Second World War where it took a few years before the Soviet Union began to use any significant force on German territory after the latter’s invasion.

The Importance of the Necessity Criterion

We agree of course with Ruys and Silvestre that there must be some proximity between attack and defence, and that the lapse of time between the two cannot be extended indefinitely. However, this argument does not go to whether there is a continuing armed attack, but rather, as they themselves admit, to the issue of whether use of force in self-defence is necessary. So, let us try and disentangle these two issues.

First, there may be a situation where a lapse of time between an armed attack an attempt to respond is merely an indication that the use of force is no longer necessary to repel it. This will be the case where the armed attack has taken place, is complete or over, and there is nothing to repel anymore, absent any occupation. Second, if an armed attack leads to occupation of territory, then it is continuing for as long as the territory is under occupation. And if years pass between the initial attack and the use of force in self-defence, that may actually mean that the use of force in self-defence is necessary precisely because the state resorting to force in self-defence has no other means to bring the armed attack and occupation to an end (a similar point is made by Corten in this video). So, the passage of time may actually show that there is no other reasonable means of bringing the armed attack and occupation to an end, rendering the use of force in self-defence the ultima ratio—which is precisely the point of the necessity requirement.

A strong argument that Ruys and Silvestre make is based on the following passage from GA Res 2625: ‘Every State likewise has the duty to refrain from the threat or use of force to violate international lines of demarcation, such as armistice lines, established by or pursuant to an international agreement to which it is a party or which it is otherwise bound to respect’. The next sentence of the same paragraph of UNGA Res 2625 says, however: ‘Nothing in the foregoing shall be construed as prejudicing the positions of the parties concerned with regard to the status and effects of such lines under their special regimes or as affecting their temporary character’ (emphasis added).

These last words, ‘temporary character’ are, we think, significant. The aforementioned passages of UNGA Res 2625 should not be construed as referring to the principle of the peaceful settlement of (territorial) disputes, but rather as referring to the principle of necessity. In particular, the latter passage underlines that, contrary to what Ruys and Silvestre argue (time runs in favour of the aggressor, to simplify), time runs ‘against’ the aggressor, as there must be a temporal limit to lines of demarcation, if these are of a ‘temporary’ character. Surely when something lasts for a quarter of a century, then its ‘temporary’ character can be called into question. So, here is the necessity point which we think UNGA Res 2625 makes: when an armistice or demarcation line is agreed, it is no longer necessary to use force: the temporary armistice line provides time to seek other means to deal with the armed attack that has taken place. But when this armistice line is no longer ‘temporary’, rather it turns into status quo, then at some point it becomes necessary again to use force in self-defence, all other means to repel the armed attack having failed.

In sum, a use of force in self-defence will only be lawful where it responds to an armed attack which is ongoing, is necessary, and uses force that is proportionate. In cases of occupation that result from a use of force, the armed attack has not only occurred but has not ceased. Necessity is often taken to refer both to the immediacy of the response in self-defence and to the notion that the use of force is a last resort. Since prolonged occupation arising out of force is a continuing attack, any requirement relating to immediacy is met and the question then turns to the last resort element of necessity. While passage of time may, and hopefully will, open up other means for bringing the occupation to an end, the very passage of years may itself be an indication that the last resort requirement is met.