Uti possidetis
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Uti possidetis (Latin for "as you possess") is a principle in international law that territory and other property remains with its possessor at the end of a conflict, unless provided for by treaty. Originating in Roman law, this principle enables a belligerent party to claim territory that it has acquired by war. The term has historically been used to legally formalize territorial conquests, for instance the annexation of Alsace-Lorraine by the German Empire in 1871.
In the early 17th century, the term was used by King James of England and Scotland to state that while he recognized the existence of Spanish authority in those regions of the Western Hemisphere where Spain exercised effective control, he refused to recognize Spanish claims to exclusive control of all territory west of longitude 46° 37' W under the Treaty of Tordesillas.
More recently, the principle has been used to establish the frontiers of newly independent states following decolonization, by ensuring that the frontiers followed the boundaries of the old colonial territories from which they emerged. This use originated in South America in the 19th century with the withdrawal of the Spanish Empire. By declaring that uti possidetis applied, the new states sought to ensure that there was no terra nullius in Spanish America when the Spanish withdrew and to reduce the likelihood of border wars between the newly independent states. In this, however, they were not wholly successful, as the War of the Pacific (1879–1883) demonstrated.
The same principle was applied to Africa and Asia following the withdrawal of European powers from those continents. In 1964 the Organisation of African Unity passed a resolution stating that the principle of stability of borders – the key principle of uti possidetis – would be applied across Africa. Most of Africa was already independent by this time, so the resolution was principally a political directive to settle disputes by treaty based on pre-existing borders rather than by resorting to force. So far, it has successfully averted border wars between African countries (the notable exception, the Eritrean-Ethiopian War of 1998-2000, had its roots in a secession from an independent African country rather than a conflict between two decolonized neighbours). On the other hand, it has led to violent and bloody civil wars among differing ethnic groups or tribes.
The principle was affirmed by the ICJ in the 1986 Case Burkina-Faso v Mali:
"[uti posidetis] is a general principle, which is logically connected with the phenomenon of obtaining 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 changing of frontiers following the withdrawal of the administering power"
