What Is Diego Garcia Atoll and Why Is It So Controversial?
A remote coral atoll's strategic military purpose is intertwined with a decades-long human rights struggle and a modern sovereignty dispute.
Diego Garcia is a remote atoll in the central Indian Ocean, situated south of the equator. It is the largest of the 60 small islands that form the Chagos Archipelago. The island lies approximately 1,796 kilometers (1,116 miles) southwest of India and 2,112 kilometers (1,312 miles) northeast of Mauritius.
Geographic and Environmental Features
Diego Garcia is distinguished as the world’s largest continuous coral atoll, a ring-shaped coral reef that encircles a lagoon. This V-shaped formation is the result of coral growth on the remnants of a sinking volcanic island. The atoll’s land rim stretches for about 40 miles, enclosing a lagoon that is approximately 13 miles long and up to 7 miles wide.
The atoll possesses a tropical climate and supports a diverse marine ecosystem. Its coral reefs are home to numerous fish species, mollusks, and sea turtles, while the island itself provides a habitat for various bird species. The ecological importance of the region was recognized when the Chagos Archipelago was declared a large Marine Protected Area (MPA).
The MPA status is complicated by the island’s other functions. A portion of the atoll was set aside for military use under a 1976 agreement and is not included within the protected zone. The ecosystem also faces threats from climate change, particularly rising sea levels which could impact the low-lying coral structure.
The Establishment of the Military Base
The strategic location of Diego Garcia in the Indian Ocean became valued during the Cold War. In 1965, the United Kingdom detached the Chagos Archipelago from its colony of Mauritius, creating a new entity called the British Indian Ocean Territory (BIOT).
A year later, in 1966, the UK and the United States signed an agreement that permitted the U.S. to construct a military base on Diego Garcia. The island’s position offered a logistical point for naval and air operations. This accord allowed the United States to build and operate a military installation on the island for an initial period of 50 years, a term that was later extended.
The facility was developed into a naval support station, an airbase, and a communications hub. It supports naval ships and submarines and is one of two U.S. bomber bases in the Indo-Pacific region. The base also functions as an anchorage for pre-positioned military supplies, enabling rapid deployment for regional operations.
Forced Eviction of the Chagossian People
Prior to the establishment of the military base, Diego Garcia and the Chagos Archipelago were home to the Chagossians, also known as the Ilois. These inhabitants were the descendants of enslaved Africans and Indian laborers who had settled on the islands in the late 18th century. They lived in small settlements, such as East Point and Minni Minni, and worked primarily on coconut plantations.
Between 1968 and 1973, the British government forcibly removed the entire Chagossian population of over a thousand residents, deporting them to Mauritius and the Seychelles to make way for the military installation. In their new locations, the displaced Chagossians faced severe hardship, including extreme poverty, unemployment, and social marginalization. This forced relocation sparked a long and arduous struggle for justice.
The Chagossian community has since engaged in a persistent campaign for the right to return to their homeland, seeking compensation and formal recognition of their unjust removal. They have pursued numerous legal challenges in British and international courts over several decades.
Current Geopolitical Status and Controversies
The sovereignty of the Chagos Archipelago remains a subject of international dispute between the United Kingdom and Mauritius. Mauritius has consistently claimed that the detachment of the archipelago in 1965 was illegal under international law.
In 2019, the International Court of Justice (ICJ) issued an advisory opinion. The court concluded that the UK’s decolonization of Mauritius was not lawfully completed and that its continued administration of the Chagos Archipelago is unlawful. This opinion was subsequently endorsed by a large majority in the United Nations General Assembly, which called on the UK to withdraw its administration, though the UK has maintained that the ruling is not legally binding.
Adding to the geopolitical complexity are persistent allegations concerning the base’s use in controversial activities. Reports have suggested its involvement in the U.S. “extraordinary rendition” program, where individuals were transferred to secret detention sites. These claims, while not officially confirmed, have fueled further debate about the operations conducted from the island.
In 2025, a treaty was signed to transfer sovereignty of the Chagos Islands from the UK to Mauritius. A provision of this agreement is that the military base on Diego Garcia will remain under British control for at least 99 years.