European States’ Obligations to Repatriate the Children Detained in Camps in Northeast Syria found in States’ responsibilities and obligations to other countries.361 Under international law, States have a duty vis-à-vis other States to readmit nationals to their territory.362 The foundation of this obligation lies in the personal and territorial sovereignty of States, as “international order presupposes that each state takes care at least of its own nationals.”363 Accordingly, the principle of reciprocity assumes that “the State of residence has the right to demand that the return to the State of origin of such aliens whom, for valid reasons it does not intend to keep on its territory, remains possible.”364 While States’ duty vis-à-vis other States to readmit their own nationals should be distinguished from whether there exists an individual right to return, 365 according to the principle of good faith, the obligation to readmit is linked to a duty not to prevent the return of the nationals.366 Therefore, under international law, States cannot compel any other State to keep their nationals through measures such as revocation of nationality367 and cancellation of travel documents, 368 or by refusing to issue substitute documents,369 or by refusing to repatriate.370 Notably, preventing the return of nationals believed to be affiliated with a terrorist organization would also go against the principle of international cooperation 361 Peter Van Krieken, “Return and Responsibility”, Volume 38, Issue 4, September 2000, p. 30. 362 Paul Weis, “Nationality and Statelessness in International Law,” Sijthoff and Noordhoff, 2nd edition, 1979, pp. 45-46. OSJI/ISI, “Draft Commentary to the Principles on Deprivation of Nationality as a Security Measure,” 2020, para. 143; Alice Edwards, “The Meaning of Nationality in International Law in an Era of Human Rights” in Alice Edwards and Laura van Waas (eds), “Nationality and Statelessness under International Law,” Cambridge University Press, 2014, pp. 11 and 35; Atle Grahl-Madsen, “Protection of Refugees By Their Country of Origin”, Yale Journal of International Law, Volume 11, Issue 2, 1986, p. 376; Kay Hailbronner, “Readmission Agreements and the Obligation on States under Public International Law to Readmit their Own and Foreign Nationals”, Heidelberg Journal of International Law, Volume 57, Issue 1, 1997, p. 1. 363 Kay Hailbronner, “Readmission Agreements and the Obligation on States under Public International Law to Readmit their Own and Foreign Nationals”, 1997, p. 1. 364 Ibid, p. 7. 365 Ibid, p. 1. 366 Ibid, p. 15. 367 “The good faith of a State which has admitted an alien on the assumption that the State of his nationality is under an obligation to receive him back would be deceived if by subsequent denationalization this duty were to be extinguished,” See: Paul Weis, “Nationality and Statelessness in International Law,” Alphen aan den Rijn: Sijthoff and Noordhoff, 2nd Edition, 1979, pp. 125-126 cited in Guy S. Goodwin-Gill, “Mr Al-Jedda, Deprivation of Citizenship, and International Law,” revised draft of a paper presented at a Seminar at Middlesex University on 14 February 2014, p. 12. See also: Alessandra Spadaro, “Repatriation of Family Members of Foreign Fighters: Individual Right or State Prerogative?,” International and Comparative Law Quarterly, 2020, p. 263; Francesca Capone, “Is Trump Right? Foreign Fighters and the States’ Obligation to Repatriate Them,” Verfassungs Blog, 10 March 2019. 368 See: Francesca Capone, “Is Trump Right? Foreign Fighters and the States’ Obligation to Repatriate Them,” 2019. 369 Kay Hailbronner, “Readmission Agreements and the Obligation on States under Public International Law to Readmit their Own and Foreign Nationals”, 1997, p. 15. 370 See also: OSJI/ISI, Principles on Deprivation of Nationality as a Security Measure, 2020, Principle 11. 64