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 otherwise provided for by treaty; if such a treaty does not include conditions regarding the possession of property and territory taken during the war, then the principle of uti possidetis will prevail. Originating in Roman law, the phrase is derived from the Latin expression uti possidetis, ita possideatis, meaning "may you continue to possess such as you do possess" (lit., "as you possess, thus may you possess"). This principle enables a belligerent party to claim territory that it has acquired by war.
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History
In the early 17th century, the term was used by England's James I 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 possession of all territory west of longitude 46° 37' W under the Treaty of Tordesillas.
More recently, the principle has been used in a modified form (see Uti possidetis juris) to establish the frontiers of newly independent states following decolonization, by ensuring that the frontiers followed the original 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 South America when the Spanish withdrew and to reduce the likelihood of border wars between the newly independent states and the establishment of new European colonies.
The same principle was applied to Africa and Asia following the withdrawal of European powers from those continents, and in locations such as the former Yugoslavia and the Soviet Union where former centralized governments fell, and constituent states gained independence. 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. To date, adherence to this principle has allowed African countries to avoid border wars; 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, the colonial boundaries often did not follow ethnic lines, and this has helped lead to violent and bloody civil wars among differing ethnic groups in many post-colonial (and post-Communist) countries, including Sudan, the Democratic Republic of the Congo, Angola, Nigeria, Uganda, Georgia, Azerbaijan, Moldova and the former Yugoslavia.
The principle was affirmed by the International Court of Justice in the 1986 Case Burkina-Faso v Mali:
[Uti possidetis] 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.