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II. Substantive International Law - Second Part
1.2. Boundaries
1.2.4.Principle of "uti possidetis"

¤ Frontier Dispute, Judgment
(Burkina Faso/Republic of Mali)
I.C.J. Reports 1986, p. 554

[pp. 565-567] Since the two Parties have, as noted above, expressly requested the Chamber to resolve their dispute on the basis, in particular, of the "principle of the intangibility of frontiers inherited from colonization", the Chamber cannot disregard the principle of uti possidetis juris, the application of which gives rise to this respect for intangibility of frontiers. Although there is no need, for the purposes of the present case, to show that this is a firmly established principle of international law where decolonization is concerned, the Chamber nonetheless wishes to emphasize its general scope, in view of its exceptional importance for the African continent and for the two Parties. In this connection it should be noted that the principle of uti possidetis seems to have been first invoked and applied in Spanish America, inasmuch as this was the continent which first witnessed the phenomenon of decolonization involving the formation of a number of sovereign States on territory formerly belonging to a single metropolitan State. Nevertheless the principle is not a special rule which pertains solely to one specific system of international law. It is a general principle, which is logically connected with the phenomenon of the obtaining of independence, wherever it occurs. Its obvious purpose is to prevent the independence and stability of new States being endangered by fratricidal struggles provoked by the challenging of frontiers following the withdrawal of the administering power.
It was for this reason that, as soon as the phenomenon of decolonization characteristic of the situation in Spanish America in the 19th century subsequently appeared in Africa in the 20th century, the principle of uti possidetis, in the sense described above, fell to be applied. The fact that the new African States have respected the administrative boundaries and frontiers established by the colonial powers must be seen not as a mere practice contributing to the gradual emergence of a principle of customary international law, limited in its impact to the African continent as it had previously been to Spanish America, but as the application in Africa of a rule of general scope.
The elements of uti possidetis were latent in the many declarations made by African leaders in the dawn of independence. These declarations confirmed the maintenance of the territorial status quo at the time of independence, and stated the principle of respect both for the frontiers deriving from international agreements, and for those resulting from mere internal administrative divisions. The Charter of the Organization of African Unity did not ignore the principle of uti possidetis, but made only indirect reference to it in Article 3, according to which member States solemnly affirm the principle of respect for the sovereignty and territorial integrity of every State. However, at their first summit conference after the creation of the Organization of African Unity, the African Heads of State, in their Resolution mentioned above (AGH/ Res. 16 (I)), adopted in Cairo in July 1964, deliberately defined and stressed the principle of uti possidetis juris contained only in an implicit sense in the Charter of their organization.
There are several different aspects to this principle, in its well-known application in Spanish America. The first aspect, emphasized by the Latin genitive juris, is found in the pre-eminence accorded to legal title over effective possession as a basis of sovereignty. Its purpose, at the time of the achievement of independence by the former Spanish colonies of America, was to scotch any designs which non-American colonizing powers might have on regions which had been assigned by the former metropolitan State to one division or another, but which were still uninhabited or unexplored. However, there is more to the principle of uti possidetis than this particular aspect. The essence of the principle lies in its primary aim of securing respect for the territorial boundaries at the moment when independence is achieved. Such territorial boundaries might be no more than delimitations between different administrative divisions or colonies all subject to the same sovereign. In that case, the application of the principle of uti possidetis resulted in administrative boundaries being transformed into international frontiers in the full sense of the term. This is true both of the States which took shape in the regions of South America which were dependent on the Spanish Crown, and of the States Parties to the present case, which took shape within the vast territories of French West Africa. Uti possidetis, as a principle which upgraded former administrative delimitations, established during the colonial period, to international frontiers, is therefore a principle of a general kind which is logically connected with this form of decolonization wherever it occurs.
The territorial boundaries which have to be respected may also derive from international frontiers which previously divided a colony of one State from a colony of another, or indeed a colonial territory from the territory of an independent State, or one which was under protectorate, but had retained its international personality. There is no doubt that the obligation to respect pre-existing international frontiers in the event of a State succession derives from a general rule of international law, whether or not the rule is expressed in the formula uti possidetis. Hence the numerous solemn affirmations of the intangibility of the frontiers existing at the time of the independence of African States, whether made by senior African statesmen or by organs of the Organization of African Unity itself are evidently declaratory rather than constitutive: they recognize and confirm an existing principle, and do not seek to consecrate a new principle or the extension to Africa of a rule previously applied only in another continent.
However, it may be wondered how the time-hallowed principle has been able to withstand the new approaches to international law as expressed in Africa, where the successive attainment of independence and the emergence of new States have been accompanied by a certain questioning of traditional international law. At first sight this principle conflicts outright with another one, the right of peoples to self-determination. In fact, however, the maintenance of the territorial status quo in Africa is often seen as the wisest course, to preserve what has been achieved by peoples who have struggled for their independence, and to avoid a disruption which would deprive the continent of the gains achieved by much sacrifice. The essential requirement of stability in order to survive, to develop and gradually to consolidate their independence in all fields, has induced African States judiciously to consent to the respecting of colonial frontiers, and to take account of it in the interpretation of the principle of self-determination of peoples.
Thus the principle of uti possidetis has kept its place among the most important legal principles, despite the apparent contradiction which explained its coexistence alongside the new norms. Indeed it was by deliberate choice that African States selected, among all the classic principles, that of uti possidetis. This remains an undeniable fact. In the light of the foregoing remarks, it is clear that the applicability of uti possidetis in the present case cannot be challenged merely because in 1960, the year when Mali and Burkina Faso achieved independence, the Organization of African Unity which was to proclaim this principle did not yet exist, and the above-mentioned resolution calling for respect for the preexisting frontiers dates only from 1964.

[p. 568] By becoming independent, a new State acquires sovereignty with the territorial base and boundaries left to it by the colonial power. This is part of the ordinary operation of the machinery of State succession. International law - and consequently the principle of uti possidetis - applies to the new State (as a State) not with retroactive effect, but immediately and from that moment onwards. It applies to the State as it is, i.e., to the "photograph" of the territorial situation then existing. The principle of uti possidetis freezes the territorial title; it stops the clock, but does not put back the hands. Hence international law does not effect any renvoi to the law established by the colonizing State, nor indeed to any legal rule unilaterally established by any State whatever; French law - especially legislation enacted by France for its colonies and territoires d'outre-mer - may play a role not in itself (as if there were a sort of continuum juris, a legal relay between such law and international law), but only as one factual element among others, or as evidence indicative of what has been called the "colonial heritage", i.e., the "photograph of the territory" at the critical date.

[pp. 586-587] Apart from the texts and maps listed above, the Parties have invoked in support of their respective contentions the "colonial effectivités", in other words, the conduct of the administrative authorities as proof of the effective exercise of territorial jurisdiction in the region during the colonial period. For Burkina Faso, the effectivités can support an existing title, whether written or cartographical, but when their probative value has to be assessed they must be systematically compared with the title in question; in no circumstances can they be substituted for the title. For its part, Mali admits that in principle the effectivités cannot be brought into operation where they are contrary to the text of a treaty, but argues that in a situation where there is no boundary described in conventional or legislative form, it is necessary to ascertain the boundary by other methods, and an investigation of the effectivités then becomes essential. The role played in this case by such effectivités is complex, and the Chamber will have to weigh carefully the legal force of these in each particular instance. It must however state forthwith, in general terms, what legal relationship exists between such acts and the titles on which the implementation of the principle of uti possidetis is grounded. For this purpose, a distinction must be drawn among several eventualities. Where the act corresponds exactly to law, where effective administration is additional to the uti possidetis juris, the only role of effectivité is to confirm the exercise of the right derived from a legal title. Where the act does not correspond to the law, where the territory which is the subject of the dispute is effectively administered by a State other than the one possessing the legal title, preference should be given to the holder of the title. In the event that the effectivité does not co-exist with any legal title, it must invariably be taken into consideration. Finally, there are cases where the legal title is not capable of showing exactly the territorial expanse to which it relates. The effectivités can then play an essential role in showing how the title is interpreted in practice.

[pp. 661-662 S.O. Abi-Saab] The purpose of this frantic search for a "written legal title", turning anything and everything into account, is to satisfy a particular conception of the uti possidetis principle.
However, this principle, like any other, is not to be conceived in the absolute; it has always to be interpreted in the light of its function within the international legal order.
At first sight, it may indeed seem paradoxical that peoples that have struggled for their independence should set so much store by their "colonial heritage". At the beginning, however, at the time when the Latin American countries were achieving independence, the principle of uti possidetis was formulated to serve a dual purpose: first, a defensive purpose towards the rest of the world, in the form of an outright denial that there was any land without a sovereign (or terra nullius) in the decolonized territories, even in unexplored areas or those beyond the control of the colonizers; secondly, a preventive purpose: to avoid or at least to minimize conflict occurring in the relationships among the successors, by freezing the carved-up territory in the format it exhibited at the moment of independence.

These two objectives therefore postulate the existence of a boundary, an impermeable territorial division, at the moment of independence. This hypothesis can only be factually verified in each case if a boundary is taken to mean a "line" in the geometric sense of the word. Otherwise it will be the inevitable fate of the principle of uti possidetis to operate as a mere fiction that jars with reality.

This is because a minimum of two points will always suffice for the definition of a line if one starts from the geometric concept of a "line" as "generated by the motion of a point" (Encyclopaedia Britannica, 11th ed.). In this sense there would always be a line to satisfy the logical requirements for the functioning of the uti possidetis principle. But if one starts from the common idea of a line as a concrete trace every point on which is specifically identifiable, it is far from likely that the postulate could be shown as realized in every instance.
By proceeding from the geometric concept of a line, which is alone capable of reconciling the principle of uti possidetis with the facts, we can state that there is always a line which defines the outer limit of lawful possession. But the scope of a court's role in identifying that line will vary inversely to the extent of its having taken concrete shape. The fewer the points (or points of reference) involved in its definition, the greater the court's "degrees of freedom" (in the statistical sense). And it is here that considerations of equity infra legem (mentioned in paragraph 28 of the Judgment) come into play, to guide the court in the exercise of this freedom when interpreting and applying the law and the legal titles involved.