evidence: Various contributors to The Interpreter’s Chagos Question debate assert that Britain’s controversial claim to the Chagos Archipelago (British Indian Ocean Territory – BIOT) violates the rules-based order. And by extension, Australian and American support for London’s colonial-era sovereignty pretension further undermines this already fragile Indo-Pacific order. [...] The Chagos Archipelago was historically administered as part of the Colony of Mauritius. Its separation in 1965 was in violation of the customary international law that pertained at the time. This law had crystalised the territorial integrity of non-self-governing territories as a key element of the exercise of the right to self-determination. It follows from this that the Chagos Archipelago shouldn’t have been separated from Mauritius at the time of its Cold War-era independence. It is this principle of respecting the territorial integrity of former colonies that the United Kingdom violated in establishing BIOT, demonstrating disregard for one of the most fundamental tenets of the rules-based order and of international law as established post-1945. [...] For Britain to satisfy its commitment to the rules-based order and international law, its only option is to dissolve BIOT and cede sovereignty of the Chagos to Mauritius. Otherwise, this ugly episode of international affairs will continue to undermine the already fragile rules-based order, threatening its provision of public goods, including rule of international law.