In 1962 Dean Acheson, US Secretary of State under the Truman administration, made a speech in which he described Britain as having ‘lost an empire … but not yet found a role.’ Decades later, the UK is still attempting to find its footing in an unstable and shifting geopolitical context. The post-Brexit promise of Global Britain has given way to an emphasis on the linkages between economic and national security to meet the rising threat of China and the fragmentation of global trade. Now with Donald Trump’s re-election, a rapid and seismic shift in Euro-Atlantic diplomacy has taken place. The implications for Britain are apparent in its attempts to reach an agreement over the Chagos Islands.

In early April 2025, Keir Starmer’s government announced it had received approval from the United States for its agreement with Mauritius to hand back the 58 atolls comprising British Indian Ocean Territory, in exchange for a ninety-year lease of Diego Garcia. In the last year, the UK has found it difficult to provide a clear rationale for its agreement with Mauritius. The cost of the agreement has been widely criticized as fiscally damaging and a strategic mistake. Some have argued Britain’s agreement opens the door to Chinese covert influence over Chagos. The severity of criticism has however ignored the wider geopolitical and strategic imperatives driving the UK to reach this agreement. These require balancing between competing relationships, ideological imperatives, and the larger tectonic shifts of geopolitics.

Geopolitical and Historical Background

The geopolitics of British Overseas Territories have obvious roots in the legacy of British imperialism. The fourteen territories which comprise Britain’s overseas possessions span over 2000 islands across the globe. These territories are strategic assets and give the UK significant global reach in areas of the world otherwise outside of conventional foreign policy influence. Britain’s handling of the Chagos dispute has also been an important case study for maritime disputes reflecting western states desire to retain and expand in the Indo-Pacific. The UK’s changing strategy reveals much about the limits of framing maritime and sovereign disputes in terms of the international rules based order.

Britain first claimed sovereignty over Mauritius and the Chagos Islands in the early nineteenth century. In 1965, three years before Mauritius secured independence from Britain, the UK negotiated with Mauritian representatives to retain sovereignty over the Chagos archipelago, while establishing the islands as an official overseas territory. Britain treated the islands as a security asset, expelling the islands’ inhabitants, and negotiating with the United States the building of a military base on Diego Garcia, which is the largest of the atolls comprising Chagos. Mauritius began multiple decades of legal complaint that the UK had illegally separated the islands at the time of its independence. In 2019, following an advisory opinion of the International Court of Justice and a subsequent formal vote by the UN General Assembly, the long-term British occupation of the Chagos Islands was deemed to be in breach of international law. The latter in particular represented a humiliating international rebuttal of the UK’s international standing and influence.

In establishing the Diego Garcia base, the UK claimed decolonization laws were secondary to the necessity of countering threats to national security in the Indo-Pacific. Even if the nature of national security threats have changed over time, from the need to counter Soviet influence in the region, to the War on Terror, and now the rise of China, the islands’ geostrategic location has maintained a significant role in the US military network. It has been used as a hub in every major US military operation in the Near East from the 1973 Arab Israeli War, to the US invasions of Iraq, and operations in Afghanistan.

The UK, the EU, and International Law

Many have claimed the UK’s position on surrendering Chagos is explained by Starmer’s affinity for international law. However, the more important context for Chagos concerns the UK’s regional and diplomatic isolation following its withdrawal from the EU. The UN vote was a message to Britain from European allies, including France and Germany (who both abstained), that its exit from the EU entailed a loss of influence on the global stage. Britain has long benefited from the international rules based order, particularly in its capacity to build support and defend its national interests through multilateral organizations. Yet the long-term complaint of non-western states is that US-UK-EU governments adhere to international law selectively and expediently. Without European support the UK became much more vulnerable to these types of attacks. It was forced to open negotiations with Mauritius or lose credibility and influence not just with the EU but globally.

At the time of the UN vote, the EU’s relations with the UK were heavily strained. The latter faced strong criticism from the EU that it was seeking to advance its own sovereign interests, at the expense of respect for commitments to abide by legal principles. But now in 2025, the UK and EU are faced with a very different geopolitical context. UK-EU relations have changed since the invasion of Ukraine, with closer diplomatic and security co-operation seen as mutually beneficial, especially as the EU faces a much more aggressive and less co-operative stance towards European defense and security from the United States.

As both the UK and EU work to bolster European security against Russia, respect for international legal institutions and norms will remain one of the key means by which both press their strategic aims, such as territorial integrity against imperial aggression. In this context the Chagos agreement allows the UK to reconfirm its commitment to a rules-based international order, fundamental to the EU’s global standing, while pressing home its opposition to imperialism.

Britain, Chagos, and the United States

Britain’s overriding rationale for reaching an agreement is the primacy and asymmetry of its military security relationship with the United States. In 2022, as Mauritius escalated its campaign for Chagos’ return, Britain’s claims looked increasingly vulnerable and the US began to play a greater part in pressing the UK to find a resolution. In the last year of the Biden administration, the US backed the Chagos agreement, citing its support for a resolution based on international norms of sovereignty which would also secure thefree seas from Chinese expansionism.

Biden’s strategy is at odds with the first and second Trump administration’s, whose geostrategic aims reject liberal internationalism, financed by US military and economic power, as the means to counter China. This includes a much more aggressive, competitive, and transactional relationship to European allies on trade and security.

Earlier this year, the UK waited anxiously after Trump’s election to see if the Chagos agreement would find agreement in Washington. Months earlier Republican congressmen, including now Secretary of State Marco Rubio, had decried the UK’s plans as a strategic victory for China. But when Starmer visited the Whitehouse in February, Trump described his enthusiasm for the Chagos agreement, setting out his support for the length of the lease to be agreed. Public discussion of the UK paying to lease Diego Garcia for US purposes would likely have appealed to Trump’s financially transactional instincts. Indeed, Starmer’s strategy in visiting Washington was to appease Trump’s agenda in substantive terms, commiting to increase UK defense spending through cutting its aid budget, effectively recognizing the gravity of the shift in transatlantic relations.

Britain, India, and Middle Power Status

The UK is still slowly also coming to terms with the rise of the Indo-Pacific as the strategic focus of great power rivalry and middle power influence. Just as the United States and Europe have shifted strategic focus from the Atlantic to Asia, the UK has made its own pivot, framed in the 2021 Strategic Review as an ‘Indo-Pacific tilt.’ Increasingly caught between a more antagonistic US and a defensive EU, India will be a crucial future partner for the UK. Its evolving role in shaping the security architecture of the Indian Ocean has been manifest in its important behind-the-scenes role in UK-Mauritius negotiations.

Historically an unaligned power, India has drawn much closer to the United States as it seeks to counter Chinese influence over the Indo-Pacific. Chinese naval influence in the Indian Ocean is currently limited and as India seeks to shore up its maritime security presence, including closer scrutiny of shipping routes, its relationship with Mauritius will likely act as a counterbalance to the influence of China over the former. Not only a former colonial dependent of the British empire and long sympathetic to Mauritius’ anti-colonial claims to territorial integrity, it has strong ethnic and economic ties to the island nation. India has significant investment in its bilateral trade and sea and air infrastructure.

Britain clearly hopes the agreement with Mauritius will allow it to resolve one area of contention obstructing closer economic ties with India. Expanded trade and investment ties with the country have figured as a major post-Brexit prize. The impetus for such an agreement will be even greater now given the risks posed by Trump’s tariff policies.

An Exercise in Triangulation

It is hard to see how the UK could have navigated these three geopolitical contexts without damage to its international reputation, strategic security priorities, or future influence in the Indo-Pacific. There is more than a suggestion of post-imperial declinism in the criticisms of the UK’s decisions on Chagos. The UK still finds itself confronting its middle power status with some reluctance. For these reasons, the UK government’s agreement on Chagos should be judged as a successful navigation of complicated geopolitical terrain through diplomacy. Yet there remain risks to the success of Britain’s agreement. The final financial costs are yet to be confirmed and may raise further problems for the UK’s financially constrained government. Similarly, Starmer’s claim to have followed international legal obligations will look less convincing if his government fails to resolve the injustice done to the Chagos’ expelled inhabitants. Perhaps most of all, the British government will have to deal with the precedent this agreement sets in terms of its other overseas dependencies, particularly Gibraltar and the Falklands. Ironically, the successful resolution of the Chagos dispute for Britain, could open the way for further dilution of the UK’s claims to overseas sovereignty.