When the United Kingdom and Mauritius signed a historic treaty in May 2025 transferring sovereignty over the Chagos Archipelago, the headlines proclaimed a long-overdue moment of decolonisation. After decades of legal contestation, international pressure, and a landmark advisory opinion from the International Court of Justice, a colonial wrong had finally been righted. Or so the story went.

A closer look at the deal — and at the longer history it sits within — reveals a more complicated story. The 2025 treaty is a milestone, but it is also, in a precise and troubling sense, a continuation. For eighty years, strategic military interests have set the contours of decolonisation. The Chagos settlement is the latest chapter in that story, not its conclusion.

The Military Logic of Imperial Retreat

The rushed and incomplete character of British decolonisation in 1947 was not an accident but reflected the strategic and economic importance of British India. Strategically located in the middle of the Indian Ocean, British India was a military and financial reservoir for imperial defence that had proven indispensable to the Allied victory in World War II. The United States understood this acutely. On 6 November 1945, Secretary of State James F. Byrnes handed Lord Halifax, the British Ambassador to Washington, an aide-mémoire planning for post-War U.S. bases, and inviting Britain’s cooperation to realise those plans. Joint Anglo-American negotiations were proposed with the soon-to-be independent Indian government to ensure the U.S. military’s continued access. The specific sites named, the Dudhkundi and Barrackpore airports near Calcutta, and Karachi airport were both in British India in 1945.

Military bases had been a key preoccupation of Allied strategy during the Second World War. The State Department’s 1945 document listed Calcutta and Karachi as part of the string of airbases that had been built up during World War II, extending from North Africa to India and Burma. As independence approached, what would happen to that infrastructure (the airfields, the ports, the logistics networks built with enormous investment across the subcontinent) was not a secondary question.

Conscious of its decline relative to an ascendant United States, Britain rebuffed the U.S. approach regarding Indian bases. Continued domination of the Indian Ocean was explicit British policy. Naval and air bases in India were central to British imperial defence, ensuring communications between the Middle East and Africa, to the east, and between Burma, Malaya and Australia and New Zealand to the west. It was essential for Britain that the transfer of British power deliver a post-colonial regime that would be friendly to London.

Colonial officials made every attempt to maintain India’s role in imperial defence. Just weeks before he announced the partition of British India, the last Viceroy of India proposed India and Pakistan could establish a joint defence. This was not to be, and Calcutta went to post-colonial India, while Karachi went to post-colonial Pakistan. The bases near Calcutta — built with U.S. Lend-Lease and Reverse Lend-Lease funding —  were abandoned and largely forgotten as the map of South Asia was redrawn. The spatial reorganisation of decolonisation was, simultaneously, a spatial reorganisation of military power.

The partition of India and Pakistan had further consequences for the Indian Ocean’s commercial and strategic geography. The division of Bombay and Calcutta from Karachi disrupted networks that had underpinned both imperial defence and regional commerce. Decolonisation, in other words, was not a process of orderly legal transfer. It was a scramble in which military infrastructure, strategic interests, and territorial sovereignty were negotiated non-transparently and, frequently, at the expense of the populations most directly affected.

The Chagos Excision: The Same Logic, a Different Ocean

The removal of the Chagos Archipelago from Mauritius in 1965 followed the same logic with striking fidelity, and perhaps some refinement:  this time the military interest won outright.

Three years before Mauritius achieved independence, Britain detached the Chagos Archipelago from the territory that would become the new state. Twenty years after the State Department’s aide memoire, the British Indian Ocean Territory (BIOT) was created as a legal artifice, a vessel designed specifically to retain sovereignty over islands considered strategically essential to the United States. On Diego Garcia, the largest island, an existing community — the Chagossians — was forcibly removed between 1965 and 1973 to make way for a joint UK-US military base. Families were prevented from returning home after routine trips abroad, expelled with little notice, their dogs gassed with vehicle exhaust on official orders, their community of generations destroyed.

The legal architecture used to accomplish this was deliberately opaque. The excision was presented as an administrative rearrangement. Its true purpose – locking in Western military control of a critical Indian Ocean node — was not the subject of open legal scrutiny. Mauritius, negotiating its independence, had little leverage. The Cold War provided the strategic rationale; colonial-era administrative power provided the legal mechanism.

For decades, this arrangement stood, contested politically but shielded from effective legal challenge. The Chagossians fought through British courts, achieving notable but ultimately limited victories. The question of sovereignty remained unaddressed.

The ICJ Speaks: Decolonisation Was Not Completed

In 2019, the International Court of Justice finally addressed that question directly. In its Advisory Opinion the Court found, by thirteen votes to one, that the detachment had been unlawful. The process of decolonisation of Mauritius had not been completed, because the separation had not been based on the free and genuine expression of the will of the people concerned. The right to self-determination, the Court held, had been violated.

The opinion is not formally binding, but its legal and political authority was considerable. The UN General Assembly followed with Resolution 73/295, calling on the United Kingdom to end its administration of the Chagos Archipelago within six months. Britain ignored the deadline, but the legal and diplomatic ground had shifted irrevocably.

The ICJ’s finding was, in retrospect, a confirmation of what the post-war legal architecture had always implied but never directly confronted: that the right to self-determination could not be conditionally applied, that colonial powers could not carve out strategic exceptions to decolonisation while complying with its letter elsewhere. The 1965 excision had been, from the beginning, legally defective.

The 2025 Treaty: Formal Resolution, Structural Continuity

The May 2025 agreement between Mauritius and the United Kingdom formally transfers sovereignty over the Chagos Archipelago to Mauritius. On its face, it remedies the wrong the ICJ identified. And in important respects, it does represent a genuine shift: Mauritius acquires sovereign title, the BIOT ceases to exist as a legal entity, and the legal fiction that sustained British administration for sixty years is finally dissolved.

But the structural logic that produced the Chagos problem has not been dissolved alongside it.

Under the treaty, the UK retains full operational control of the Diego Garcia military base under a 99-year lease, extendable by a further 40 years. Britain will pay Mauritius £165 million per year for the first three years and £120 million per year thereafter, totalling £3.4 billion in net present value over the lease. A 24-nautical-mile buffer zone is established around Diego Garcia, within which nothing may be built without UK consent, alongside an effective UK veto on developments across the wider archipelago. The base continues to function, as it has for half a century, as one of the most strategically significant installations in the Indo-Pacific.

For the Chagossians, the deal delivers less than its framing suggests. A £40 million trust fund is to be capitalised by the UK and administered through Mauritius. But resettlement on Diego Garcia itself remains barred. The strategic interest that drove their expulsion continues to determine the limits of their return and, as the UN Special Rapporteurs observed in June 2025, the agreement was reached without the Chagossians’ consent.

The implementing legislation — the Diego Garcia Military Base and British Indian Ocean Territory Bill — has now been shelved. In January 2026 the House of Lords inserted amendments requiring a Chagossian referendum and the suspension of payments if the base became militarily inoperable; weeks later, the Trump administration withdrew its support, refusing the formal exchange of letters needed to amend the 1966 UK-US base treaty. In April 2026 the UK government paused the Bill from its legislative timetable, with no plans to reintroduce it. The treaty is signed but cannot be ratified.

Decolonisation, here as elsewhere, moves at the pace that metropolitan and great-power politics permit. The parallels to the 1947 partition of British India, involving 17 million of dead and some 3 million displaced South Asians, are evident in the displacement of more than 2,000 Chagossians, but also in the promise of a referendum. In 1948 the United Nations recommended a referendum to resolve the disputed status of Kashmir. But this has never materialised. Instead, the successor states of British India have been at odds since then, most recently in May 2025.

The Longue Durée of an Unfinished Process

From Barrackpore to Diego Garcia, from 1945 to 2025, a consistent pattern is visible. Decolonisation has never been primarily a legal event. It has been a negotiation — an unequal one — between the formal requirements of international law and the strategic interests of departing imperial powers and their allies.

The law has, over time, caught up. The ICJ opinion, and the 2025 treaty it helped to produce, represent genuine legal progress. The right to self-determination has been vindicated in principle; sovereignty has been restored on paper. These are not trivial achievements.

And yet, imperial logic still prevails. The Trump administration wants to overturn these incremental steps. In his February 2026 address to the Munich Security Conference, Marco Rubio described the post-war retreat of empire as the ‘terminal decline’ of Western civilisation. Decolonisation, in this view, was not a vindication of self-determination but a strategic catastrophe to be reversed.

The military geography has barely moved. Diego Garcia remains, as it has been since 1971, a critical node in Western power projection across the Indian Ocean and beyond. The terms negotiated in 2025 would have entrenched that position for at least a century; the terms now extant — sovereignty unratified, base unchanged — entrench it indefinitely. The Chagossians remain excluded from their ancestral homes. The financial terms once on the table, however substantial, bore a discomforting resemblance to the colonial-era arrangements that international law was designed to supersede.

The 2025 treaty was offered as the best available resolution to a problem created by the worst impulses of the decolonisation era. It would have satisfied the formal requirements the ICJ identified. Whether it would have satisfied the deeper demands of decolonisation is a different question — and one that has, for the moment, been settled by Washington’s veto rather than by Mauritius, by the Chagossians, or by the World Court. History, on current evidence, suggests we should not mistake formal closure for substantive resolution; nor, it now seems, should we assume that even formal closure is available.

The term ‘decolonisation’ itself flattens temporalities that are anything but flat: earlier nineteenth-century struggles in Central and South America, ongoing struggles in Palestine and New Caledonia, and the rushed and violent partition of British India in 1947 whose security aftershocks are still being felt. As Ann Laura Stoler has argued, imperial retreat did not abolish empire’s sovereignty forms so much as redistribute and recompose them: graded, overlapping, partial sovereignties; sovereignty conditional on the base, on the lease, on the buffer zone. Diego Garcia is one such re-composition: the 2025 treaty, had it been ratified, would have been another. The post-war global order built on national sovereignty has always coexisted with these imperial residues, and the Trump administration’s openly stated intention to ‘reform’ that order should be read as a proposal to make imperial calculations primary again. From Barrackpore to Diego Garcia, the lesson is the same: where the base goes, sovereignty bends

Alberto Rinaldi is Assistant Professor of International Law at Lund University, Sweden. His research explores how law interacts with technology, culture, and emotions. LinkedIn

Atiya Hussain is Associated Researcher in the Department of History at the University of Zurich, Switzerland. She studies the transnational linkages of post-War decolonization and global finance. LinkedIn