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Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (I.C.J.)

  • Stephen Allen (a1)


In its Chagos Advisory Opinion, the International Court of Justice (ICJ) addressed two questions posed in a request from the UN General Assembly. First, had Mauritius's decolonization been completed when it gained independence in 1968, after the excision of the Chagos Archipelago? Second, what were the legal consequences flowing from the United Kingdom's continued administration of the Archipelago? It was thought that the Court might shy away from giving an Opinion in this case as, arguably, it concerned a bilateral sovereignty dispute that the United Kingdom had not agreed to have resolved by judicial decision. However, as it turned out, the Court delivered surprisingly robust responses to the questions posed. The Opinion—and the numerous Separate Opinions that accompanied it—offer a thorough re-evaluation of the customary international law (CIL) concerning the right to self-determination in cases of decolonization.



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1 Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Feb. 25, 2019), [hereinafter Opinion].

2 GA Res. 71/292 (Jun. 22, 2017).

3 On May 22, 2019, the General Assembly adopted Resolution 73/295, which welcomed the Court's Advisory Opinion and demanded, inter alia, the United Kingdom's unconditional withdrawal from the Chagos Archipelago within six months. The voting record was 116-6-56.

4 Mauritius was listed as a Non-Self-Governing Territory in GA Res. 66(I) (Dec. 14, 1946). See UN Charter art. 73.

5 See Stephen Allen, The Chagos Islanders and International Law (2014).

6 United Nations Convention on the Law of the Sea, Dec. 10, 1982, 1833 UNTS 39.

7 Chagos Marine Protected Area (Mauritius v. U.K.), Award (Annex VII LOSC Tribunal, Perm. Ct. Arb. 2015). However, Judges Katega and Wolfrum reached the opposite conclusion.

8 In particular, Articles 2(3), 56(2), and 194(4) of UNCLOS. However, the MPA remains in force as a matter of U.K. law. See R (Bancoult No. 3) v. Secretary of State for Foreign and Commonwealth Affairs, U.K. Supreme Court (2018), 57 ILM 671 (2018).

9 See Western Sahara Advisory Opinion 1975 ICJ Rep. 12, ¶¶ 32–33 (Oct. 16) [hereinafter Western Sahara].

10 GA Res. 1514(XV) (Dec. 14, 1960). See also GA Res. 2066(XX) (Dec. 16, 1965) on Mauritius.

11 GA Res. 2625(XXV) (Oct. 24, 1970). See, e.g., Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965, Verbatim Record, 45 (Sept. 3, 2018, 3 p.m.),

12 North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark and Netherlands), 1969 ICJ Rep. 3, 43 (Feb. 20).

13 See International Law Association, Statement of Principles Applicable to the Formation of General Customary International Law 41 (2000),

14 See id at 19 for the ILA's view regarding the practice of international organizations as “State practice.”

15 Opinion, supra note 1, ¶¶ 150–53.

16 Id. ¶ 160; Western Sahara, supra note 8, ¶ 59.

17 Opinion, supra note 1, ¶ 160.

18 Id. ¶ 172.

19 Id. ¶ 174 (13 votes to 1).

20 Id. ¶ 177 (13 votes to 1).

21 Id. ¶ 180. See East Timor (Portugal v. Aus.) Judgment, 1995 ICJ Rep. 102, ¶ 29 (Jun 30).

22 See the International Law Commission's Articles on Responsibility of States for Internationally Wrongful Acts (2001) (ARSIWA) [hereinafter ARSIWA], arts. 40 and 41(2). Judges Trindade and Robinson argued that the ICJ should have endorsed self-determination's peremptory nature.

23 See id. art. 16.

24 Opinion, supra note 1, ¶¶ 178–79.

25 Id. ¶ 180.

26 See ARSIWA, supra note 21, art. 14.

27 The United Kingdom's initial response to the Opinion has not been positive. See Statement by the Minister of State for Foreign Affairs, House of Commons (Feb. 26, 2019).


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