Uti possidetis juris

Uti possidetis juris or uti possidetis iuris (Latin for "as you possess under law") is a principle of international law which provides that newly-formed sovereign states should retain the internal borders that their preceding dependent area had before their independence.
History.
"Uti possidetis juris" is a modified form of "uti possidetis"; created for the purpose of avoiding "terra nullius", the original version of "uti possidetis" began as a Roman law governing the rightful possession of property. During the medieval period it evolved into a law governing international relations and has recently been modified for situations of newly independent states.
Application.
"Uti possidetis juris" has been applied in modern history to such regions as South America, Africa, the Soviet Union, and numerous other regions where centralized governments were broken up, or where imperial rulers were overthrown. It is often applied to prevent foreign intervention by eliminating any contested "terra nullius", or no man's land, that foreign powers could claim, or to prevent disputes that could emerge with the possibility of redrawing the borders of new states after their independence.
Argentina and Chile base their territorial claims in Antarctica on the "uti possidetis juris" principle in the same manner as their now recognized Patagonian claims.