Delimitation Before Decolonization: A Legal Contradiction in the ITLOS Ruling on Chagos

ITLOS Case no. 28: the Special Chamber

MC-BRIEF 01: The ITLOS decision in the Mauritius v. Maldives maritime delimitation case (2021–2023) highlights a significant and unresolved tension that exists between the principle of decolonisation and the legal prescriptions for naval delimitation under UNCLOS. At the core of this contradiction is the court's determination to view Mauritius as the coastal state that enjoys EEZ and continental shelf rights around the Chagos Archipelago, notwithstanding the archipelago's colonial status and the system's lack of effective Mauritian control.

1. UNCLOS and Coastal State Rights: Some Aspects of a Misalliance of Legal Instruments
According to UNCLOS (United Nations Convention on the Law of the Sea), the claim and delimitation of maritime zones, such as the Exclusive Economic Zone (EEZ) or the continental shelf, can only be made by a coastal state. An essential and preliminary legal prerequisite is full sovereignty over the coast, from which the maritime foursquare is calculated. 

However, ITLOS ruled that Mauritius was entitled to the maritime rights around Chagos before the actual decolonisation, a seriously stretched interpretation of UNCLOS. Mauritius did not have an effective administration, legal, or military presence in the Chagos Islands during the time of the ruling. The UK remained in control, and there was no formal handover process.

It turned the history of decolonisation and delimitation upside down, making prospective or aspirational sovereignty (based on the ICJ advisory opinion) appear as though it were actual and effective sovereignty within the meaning of UNCLOS. This would be a flagrant violation of the Vienna principle of ex injuria jus non oritur (no legal right arises from an illegal act), and would further undermine both decolonisation law and the law of the sea.

2. Decolonisation is not a Legal Creation
The ICJ's 2019 opinion held that the UK's continued administration of the Chagos Archipelago was illegal and that the decolonisation of Mauritius had not been completed correctly in 1968. However, the opinion is advisory and has no binding legal force. Chagos remains under the physical sovereignty of the UK.

In treating this non-binding ICJ opinion as equivalent to recognition of Mauritian sovereignty by default, ITLOS short-circuited the decolonisation process, sidestepping the need for a formal, complete transfer of sovereignty. This turns decolonisation from a political reality into a legal fiction, disempowering the UN and trampling on the self-determination of others, not least the Maldives, which were never consulted when the Chagos Islands were initially detached, and which have their own historical claim to the territory.

3. Redefined Boundaries but not decolonisation: A dangerous precedent
By granting Mauritius the maritime rights around Chagos before actual decolonisation, this litigation sets a perilous precedent: It permits a state that effectively lacks sovereignty to make full naval claims of a sovereign state. It promotes the legal weaponisation of ICJ advisory opinions to gain a geopolitical advantage. This risks construing end-to-end UNCLOS jurisprudence, replacing coherence with ad hoc case improvisation. By acting in this way, ITLOS not only grants itself more judicial powers, but also effectively upholds a landless status in which the sovereignty of a territory can be assumed based on will rather than fact. This erodes international stability and the ideals of fairness and justice that decolonisation is supposed to promote.

4. Maldives: The Unspoken Casualty Of Judicial Overreach
The Maldives – right next door, but an independent country since 1965 – ended up being collateral damage in this relaunched legal saga. Its claims, based on historical presence, geographic proximity, and the principle of non-recognition of unsettled sovereignty, were rejected. This effectively imposed judicial fiat delimitation, ignoring legitimate disputes and silencing difficulties within the aegis of enforcing an unfinished decolonisation.

Conclusion: Decolonisation Can't Be Determined By Delimitation
ITLOS was wrong not just in law but in logic. You cannot circumscribe before you decolonise. To reverse that order of being is to legitimise fiction as fact, and to conflate political aspiration with judicial entitlement. In the rush to save Mauritius, the tribunal compromised procedural regularity, the principle of equality among states, and historical justice.

In the end, the ITLOS decision holds a mirror up to what has become a studious tradition of judicial overreach in the guise of anti-colonialism, effectively claiming to work for decolonisation but doing the opposite.