Chagos Archipelago

Also called: Diego Garcia · Topic: World Physical Features and Natural Regions · NCERT: Beyond NCERT

Meaning

The Chagos Archipelago is a group of islands in the central Indian Ocean, south of the Maldives. Its largest island is Diego Garcia, which has a US-UK military base. Diego Garcia is one island in the group. It is not another name for the whole archipelago.

It matters because it was the last big decolonisation dispute in the Indian Ocean. In a 2025 treaty, the UK agreed to give sovereignty (legal ownership) of Chagos to Mauritius. The UK keeps the Diego Garcia base on a 99-year lease. Check the latest ratification status of the treaty.

Explanation

What kind of islands they are

• Archipelago: a group or chain of islands. Lakshadweep, the Maldives and Chagos are all examples.
• The islands are coral atolls. An atoll is a ring-shaped coral reef around a lagoon.
• The islands are low and flat, like the atolls of Lakshadweep and the Maldives.

• All three groups lie along the same line of undersea ridge, running north to south through the Arabian Sea and the central Indian Ocean.

• Why the location matters: Chagos sits near the middle of the Indian Ocean. A base there can reach the sea lanes of the Arabian Sea, the Gulf and South-east Asia. That is why Diego Garcia became a military base.

How the dispute started (cause → process → result)

• 1965: separation. Britain cut Chagos off from colonial Mauritius. It named the islands the "British Indian Ocean Territory".
• 1968: incomplete independence. Mauritius became independent, but without Chagos. The islanders, called Chagossians, were later moved out.
• Result: Mauritius said its independence was never complete. Chagos became a disputed territory between the UK and Mauritius.

How it was settled: the legal path

• 25 February 2019: ICJ advisory opinion.
• The court said Mauritius's decolonisation was not lawfully completed in 1968.
• The UK must end its rule over Chagos "as rapidly as possible".

• All UN members must help finish the decolonisation [2].

• ICJ advisory opinion: a legal opinion from the International Court of Justice, given when a UN body asks for one.

• It is not legally binding.

• It still carries great moral and legal weight.

• 22 May 2019: UNGA resolution 73/295.

• It welcomed the ICJ opinion.
• It said Chagos is an integral part of Mauritius.
• It asked the UK to withdraw within six months [2][3].
• The vote was 116 for, 6 against and 56 abstentions [2][3].

• The six against were Australia, Hungary, Israel, the Maldives, the UK and the USA [2].

• 2025: UK-Mauritius treaty.

• Sovereignty passes to Mauritius.
• The UK keeps the Diego Garcia base on a 99-year lease.

India's position

• India supported Mauritius and voted for resolution 73/295.
• This fits India's long support for decolonisation, which means ending colonial rule.
• It also fits India's close ties with Mauritius:
• SAGAR (2015): "Security and Growth for All in the Region". India announced it in Mauritius.
• MAHASAGAR (March 2025): "Mutual and Holistic Advancement for Security and Growth Across Regions". PM Modi launched it during his visit to Mauritius [4][5].
• In March 2025, India-Mauritius ties became an "Enhanced Strategic Partnership" [4].

Where it occurs

• Chagos Archipelago: central Indian Ocean, south of the Maldives.
• Diego Garcia: the largest island of Chagos. It has the US-UK military base.
• Mauritius: the island country in the south-west Indian Ocean. It now holds sovereignty over Chagos under the 2025 treaty.
• India's nearby island chain, from north to south, along the same line of atolls:
• Lakshadweep (Arabian Sea). The Nine Degree Channel separates the main Lakshadweep islands from Minicoy.
• The Eight Degree Channel separates Minicoy from the Maldives.

• Chagos lies further south of the Maldives.

• Other Indian Ocean islands for comparison:

• Agalega (Mauritius, western Indian Ocean)
• Reunion (France)
• Cocos (Keeling) and Christmas Island (Australia)
• Socotra (Yemen)

Don't confuse with

• Agalega Islands: two small islands that already belong to Mauritius, about 1,100 km north of the main island. India paid for an airstrip and the St. James Jetty there, opened on 29 February 2024 [1]. Agalega was never disputed. Chagos was.
• Falklands / Malvinas: a UK island dispute with Argentina in the south-west Atlantic, and it is still unresolved. Chagos is in the Indian Ocean, and the 2025 treaty is settling it.
• Maldives: an independent coral-atoll country north of Chagos. Trap: the Maldives voted against resolution 73/295, even though it is an Indian Ocean neighbour [2].
• ICJ advisory opinion vs ICJ judgment: the 2019 Chagos ruling was an advisory opinion, which is not legally binding. A judgment in a case between two countries is binding on them.

Prelims Hooks

• Diego Garcia is the largest island of the Chagos Archipelago in the central Indian Ocean. It has a US-UK military base.
• 1965: Britain separated Chagos from Mauritius and called it the "British Indian Ocean Territory".
• ICJ advisory opinion, 25 February 2019: Mauritius's decolonisation was not lawfully completed [2]. The opinion is not binding.
• UNGA resolution 73/295 (22 May 2019): passed 116–6, with 56 abstentions [2][3].
• Which countries voted against 73/295? The UK, USA, Australia, Hungary, Israel and the Maldives [2]. India voted for it.
• 2025 treaty: sovereignty goes to Mauritius, and the UK keeps Diego Garcia on a 99-year lease. Trap: Chagos is not linked to Seychelles, and Agalega is a separate group of Mauritian islands [1].

Mains Points

• Decolonisation and international law (GS-II):
• The case moved from the 1965 separation to the ICJ opinion (2019), then UNGA 73/295, and finally the 2025 treaty [2][3].
• It shows that a non-binding advisory opinion, backed by a large UN vote, can build enough pressure for a negotiated settlement.

• India's support for Mauritius fits its anti-colonial position and builds trust with small island states.

• Strategic geography of the Indian Ocean (GS-I, GS-III):

• Chagos sits in the middle of the Indian Ocean, so the Diego Garcia base watches over major sea lanes.
• The treaty keeps the base but changes who owns the islands. This brings Mauritius, a close Indian partner, into the security picture of the central Indian Ocean.

• India's other footholds work alongside this: Andaman and Nicobar near the Strait of Malacca, Lakshadweep on the Arabian Sea lanes and Agalega in the western Indian Ocean [1].

• Policy response (GS-II, GS-III):

• India moved from SAGAR (2015) to MAHASAGAR (2025), which joins security with development: trade, capacity building, concessional loans (low-interest loans) and grants [4][5].
• Low-lying coral atolls such as Chagos, the Maldives and Lakshadweep also face sea-level rise, so climate cooperation is part of this partnership.

Related concepts

• Madagascar
• Agalega Islands

Read more

• Islands and the Indian Ocean map