This article uses the history of partition to assess when self-determination became a rule of customary international law prohibiting partition as a method of decolonization. In so doing it revisits the partitions of Indochina, Korea, India, Palestine, Cyprus, South Africa, and South West Africa, and explains that UN practice underwent a transformation when the UN General Assembly opposed the United Kingdom’s partition proposals for Cyprus in 1958. Two years later, the UN General Assembly condemned any attempt aimed at the partial or total disruption of the national unity and the territorial integrity of a country in Resolution 1514 (1960).
The illegality of partition under customary international law was raised during the second phase of the South West Africa Cases (1960–1966) in respect of South Africa’s homelands policy, but the International Court of Justice (ICJ) infamously did not address the merits of those cases. The illegality of partition was also raised in the arbitration between the United Kingdom and Mauritius over the establishment of the British Indian Ocean Territory in 1965. Like the ICJ in the South West Africa Cases, the Arbitral Tribunal decided that it did not have jurisdiction to address the legality of the British excision of the Chagos Archipelago from Mauritius, even though the legality of the excision was argued at length between counsels for Mauritius and the United Kingdom in their oral pleadings and written statements.
However, in their joint dissenting opinion, Judge Rüdiger Wolfrum and Judge James Kateka expressed their opinion that self-determination had developed before 1965, and that consequently the partition was unlawful. This paper agrees that selfdetermination prohibited the partition of Mauritius to establish the British Indian Ocean Territory, a new colony, in 1965 although self-determination probably did not emerge as a rule of customary international law until the adoption of the human rights covenants in 1966, after the excision of the Chagos Archipelago in 1965, but before the passage of the Mauritius Independence Act in 1968.