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Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965

Overview of the case

On 22 June 2017 the General Assembly adopted resolution 71/292, in which, referring to Article 65 of the Statute of the Court, it requested the Court to render an advisory opinion on the following questions:

“(a) Was the process of decolonization of Mauritius lawfully completed when Mauritius was granted independence in 1968, following the separation of the Chagos Archipelago from Mauritius and having regard to international law, including obligations reflected in General Assembly resolutions 1514 (XV) of 14 December 1960, 2066 (XX) of 16 December 1965, 2232 (XXI) of 20 December 1966 and 2357 (XXII) of 19 December 1967?;
(b) What are the consequences under international law, including obligations reflected in the above-mentioned resolutions, arising from the continued administration by the United Kingdom of Great Britain and Northern Ireland of the Chagos Archipelago, including with respect to the inability of Mauritius to implement a programme for the resettlement on the Chagos Archipelago of its nationals, in particular those of Chagossian origin?”

Thirty-one Member States of the United Nations and the African Union filed written statements, and ten States and the African Union filed written comments on the written statements. Ten States and the African Union subsequently presented written comments on these written statements. Twenty‑one States and the African Union participated in the oral proceedings, which took place from 3 to 6 September 2018.

In its Advisory Opinion delivered on 25 February 2019, the Court concluded that “the process of decolonization of Mauritius was not lawfully completed when that country acceded to independence” and that “the United Kingdom is under an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible”. Before reaching this conclusion, the Court first addressed the question of whether it possessed jurisdiction to give the advisory opinion requested by the General Assembly. Having established that it did have jurisdiction to render the advisory opinion requested, the Court examined the question, raised by a number of participants, as to whether it should nevertheless decline to exercise that jurisdiction as a matter of discretion. It concluded that, in light of its jurisprudence, there were “no compelling reasons for it to decline to give the opinion requested by the General Assembly”.

After examining the factual circumstances surrounding the separation of the archipelago from Mauritius, as well as those relating to the removal of the Chagossians from this territory, the Court addressed the questions submitted to it by the General Assembly, having found that there was “no need to reformulate the questions submitted to it for an advisory opinion in [the] proceedings”.

In examining the first question, the Court turned to the nature, content and scope of the right to self-determination applicable to the process of decolonization of Mauritius. It began by recalling that, having made respect for the principle of equal rights and self-determination of peoples one of the purposes of the United Nations, the Charter included provisions that would enable non-self-governing territories ultimately to govern themselves. Moreover, the Court noted that “the adoption of resolution 1514 (XV) represents a defining moment in the consolidation of State practice on decolonization” and that “[b]oth State practice and opinio juris at the relevant time confirm the customary law character of the right to territorial integrity of a non-self-governing territory as a corollary of the right to self-determination”. The Court considered that the peoples of non-self-governing territories are entitled to exercise their right to self-determination in relation to their territory as a whole, the integrity of which must be respected by the administering Power. After having examined the functions of the General Assembly in matters of decolonization, the Court also considered, in its analysis of the international law applicable to the process of decolonization of Mauritius, the obligations reflected in General Assembly resolutions mentioned in the first question before the Court. In the Court’s view, “by inviting the United Kingdom to comply with its international obligations in conducting the process of decolonization of Mauritius, the General Assembly acted within the framework of the Charter and within the scope of the functions assigned to it to oversee the application of the right to self-determination”. After recalling the circumstances in which the colony of Mauritius agreed in principle to the detachment of the Chagos Archipelago, the Court considered that this detachment was not based on the free and genuine expression of the will of the people concerned. It took the view that the obligations arising under international law and reflected in the resolutions adopted by the General Assembly during the process of decolonization of Mauritius required the United Kingdom, as the administering Power, to respect the territorial integrity of that country, including the Chagos Archipelago. The Court concluded that, “as a result of the Chagos Archipelago’s unlawful detachment and its incorporation into a new colony, known as the [British Indian Ocean Territory] BIOT, the process of decolonization of Mauritius was not lawfully completed when Mauritius acceded to independence in 1968”.

In addressing the second question, having established that the process of decolonization of Mauritius was not lawfully completed in 1968, the Court examined the consequences, under international law, arising from the United Kingdom’s continued administration of the Chagos Archipelago. In particular, it was of the opinion that the United Kingdom’s continued administration of the Chagos Archipelago “constitutes a wrongful act entailing the international responsibility of that State”, that the United Kingdom “has an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible, and that all Member States must co-operate with the United Nations to complete the decolonization of Mauritius”. Since respect for the right to self-determination is an obligation erga omnes, all States have a legal interest in protecting that right, the Court found. It considered that, while it is for the General Assembly to pronounce on the modalities required to ensure the completion of the decolonization of Mauritius, all Member States must co‑operate with the United Nations to put those modalities into effect. As regards the resettlement on the Chagos Archipelago of Mauritian nationals, including those of Chagossian origin, the Court was of the view that this is an issue relating to the protection of the human rights of those concerned, which should be addressed by the General Assembly during the completion of the decolonization of Mauritius.


This overview is provided for information only and in no way involves the responsibility of the Court.

Request for Advisory Opinion

Request for Advisory Opinion

23 June 2017
Request for Advisory Opinion
Available in:
English French Bilingual

Introductory Note (documents received from the Secretariat of the United Nations)

30 November 2017
Introductory Note (documents received from the Secretariat of the United Nations)
Available in:
English French

List of Documents (documents received from the Secretariat of the United Nations)

30 November 2017
List of Documents (documents received from the Secretariat of the United Nations)
Available in:
English French

Part I (documents received from the Secretariat of the United Nations)

30 November 2017
Part I (documents received from the Secretariat of the United Nations)
Available in:
English French

Part III (Documents received from the Secretariat of the United Nations)

30 November 2017
Part III (Documents received from the Secretariat of the United Nations)
Available in:
English French

Written proceedings

Oral proceedings

Verbatim record 2018/20

Public sitting held on Monday 3 September 2018, at 10 a.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Verbatim record 2018/21

Public sitting held on Monday 3 September 2018, at 3 p.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Verbatim record 2018/22

Public sitting held on Tuesday 4 September 2018, at 10 a.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Verbatim record 2018/23

Public sitting held on Tuesday 4 September 2018, at 3 p.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Verbatim record 2018/24

Public sitting held on Wednesday 5 September 2018, at 10 a.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Verbatim record 2018/25

Public sitting held on Wednesday 5 September 2018, at 3 p.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Verbatim record 2018/26

Public sitting held on Thursday 6 September 2018, at 10.40 a.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Verbatim record 2018/27

Public sitting held on Thursday 6 September 2018, at 3 p.m., at the Peace Palace, President Yusuf presiding, on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for advisory opinion submitted by the General Assembly of the United Nations)
Available in:
Original Language

Other documents

Orders

Order of 14 July 2017

Fixing of time-limits: Presentation of the written statements and written comments on those statements
Available in:
English French Bilingual

Order of 17 January 2018

Extension of time-limits: Presentation of the written statements and written comments on those statements
Available in:
English French

Advisory opinions

Summaries of Advisory Opinions and Orders

Summary 2019/2

Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 - Summary of the Advisory Opinion
Available in:
English French

Press releases

Press release 2017/27

29 June 2017
The General Assembly of the United Nations requests an advisory opinion from the Court on the legal consequences of the separation of the Chagos Archipelago from Mauritius in 1965
Available in:
English French

Press release 2017/32

24 July 2017
Legal consequences of the separation of the Chagos Archipelago from Mauritius in 1965 (Request for Advisory Opinion) - The Court makes an Order organizing the proceedings; it fixes the time-limits for the presentation of the written statements and written comments on those statements
Available in:
English French

Press release 2018/1

18 January 2018
Legal consequences of the separation of the Chagos Archipelago from Mauritius in 1965 (Request for Advisory Opinion) - The Court decides that the African Union is likely to be able to furnish information on the question submitted to the Court and extends the time-limits for the submission of written statements and of written comments
Available in:
English French

Press release 2018/39

1 August 2018
Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for Advisory Opinion) - The Court will hold public hearings from Monday 3 to Thursday 6 September 2018
Available in:
English French

Press release 2018/44

6 September 2018
Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for Advisory Opinion) - Conclusion of public hearings - The Court to begin its deliberation
Available in:
English French

Press release 2019/5

15 February 2019
Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Request for Advisory Opinion) - The Court to deliver its Advisory Opinion on Monday 25 February 2019 at 3 p.m.
Available in:
English French

Press release 2019/9

25 February 2019
Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 - The Court finds that the process of decolonization of Mauritius was not lawfully completed when that country acceded to independence and that the United Kingdom is under an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible
Available in:
English French