Uti Possidetis Iuris and the Malvinas/Falklands: Spanish Succession and the Competing Claims

What the doctrine says

Uti possidetis iuris — Latin for "as you possess under law, so you shall continue to possess" — is a principle of customary international law that emerged from the decolonization of Spanish America in the early nineteenth century. As the Spanish empire's American territories became independent republics, the principle held that each new state's borders would follow the internal administrative boundaries that had existed under Spanish colonial law at the moment of independence, rather than being redrawn from scratch or left open to occupation. Its purpose was practical: to prevent territorial vacuums and boundary wars between the newly independent republics by fixing frontiers to a specific historical date — for most of Spanish South America, 1810.

The doctrine was later revived and generalized well beyond Latin America, most notably by the International Court of Justice (ICJ) in the 1986 Frontier Dispute (Burkina Faso/Mali) case, which applied it to former French colonies in Africa.

How Argentina applies it to the Malvinas

Argentina's claim rests on the argument that the Malvinas fell within the jurisdiction of the Viceroyalty of the Río de la Plata, the Spanish colonial administration centered in Buenos Aires. Under uti possidetis iuris, Argentina contends that when the United Provinces of the Río de la Plata declared independence in 1816, sovereignty over all territory administered by that viceroyalty — including the islands — passed to the new Argentine state, just as it did for the mainland provinces. Buenos Aires appointed a political and military governor for the islands in 1829, formalizing an administration that Argentina describes as a continuation of the inherited Spanish title, not a new claim.

On this reading, Britain's landing at Puerto Soledad in January 1833, which expelled the Argentine authorities and part of the population, is not the assertion of a prior or superior claim but an unlawful interruption of a sovereignty Argentina argues it already validly held.

The legal challenges to this argument

The doctrine's application to the Malvinas faces several substantive objections that a serious legal treatment has to acknowledge:

• Third-party effect. Uti possidetis iuris developed as a rule for settling boundaries among the newly independent Spanish American republics. The United Kingdom was never a party to that regional practice and never consented to be bound by a principle designed to resolve disputes between former Spanish colonies.
• Spain's actual control. The doctrine transfers whatever title the predecessor state actually held. Critics of Argentina's position point out that Spain's own garrison had already withdrawn from the islands in 1811, two years before Britain's 1833 action and five years before Argentine independence — raising the question of what, precisely, was "inherited" in 1816.
• A state cannot inherit what it did not hold. This is the doctrinal core of the British and academic critique: if Spanish effective authority over the islands had already lapsed, the newly independent United Provinces could not inherit a title that no longer existed to be transferred.

Where the argument stands

Uti possidetis iuris remains the central historical-legal pillar of Argentina's sovereignty claim and is invoked in its diplomatic and UN submissions. It has not been tested in binding adjudication — neither Argentina nor the United Kingdom has brought the sovereignty question before the ICJ — so no court has ruled on whether the doctrine applies to a dispute between a Latin American successor state and a non-regional colonial power. The argument therefore remains a matter of legal and historical interpretation rather than settled law.