Clara Van Thillo nationality to persons of African descent.89 Racial discrimination also plays an important role in the context of State succession, as ethnic minority groups are vulnerable to exclusion from the nationality of the newly independent State.90 Finally, discrimination may also result in arbitrary nationality deprivation on other grounds, such as religion, disability, age, and sexual orientation, gender identity and gender expression, sex characteristics (SOGIESC).91 Two other causes of statelessness that were overlooked by traditional international lawyers have been identified throughout the 1990s. The first one is deficient registration of births and marriages, which was acknowledged as a cause of statelessness by UNHCR in 1997.92 Birth registration provides the legal proof of a child’s existence. While not all unregistered children are automatically stateless, it becomes more difficult to prove a child’s nationality when the child does not have a birth certificate.93 In that context, marriage registration is also important, as in many States the nationality of the spouses (and their children) is affected by marriage. Furthermore, if the marriage is unregistered, the child may be considered illegitimate and the mother may be more reluctant to register the child.94 The second newly identified cause of statelessness is migration. Migrants who are particularly vulnerable are irregular migrants, victims of human trafficking and refugees.95 For example, irregular migrants may lose their nationality due to long-term residence abroad, and may be unable to acquire the nationality of their host country as lawful residence is a general condition for naturalisation.96 Another issue is the loss of documentation, which is often the case for victims of human trafficking and refugees, who as a result cannot prove their nationality, heightening their risk of statelessness.97 In many cases, it is not one cause in isolation that renders a person stateless, but rather the concurrence of multiple factors. For example, the birth registration system may be less accessible for persons who belong to a particular ethnic minority, due to discriminatory practices.98 Registering a child may also be more difficult in the context of State succession resulting from an armed conflict, as governmental authorities may not be able to perform birth registrations.99 Migration also exacerbates other factors increasing the risk of statelessness. For example, irregular migrants face additional barriers in registering their children’s birth in their host State, such as discrimination.100 These are only a few examples of how the interaction of various factors and vulnerabilities may eventually result in statelessness. This complexity was overlooked by traditional writers. These newly identified causes of statelessness show that quite some progress has been made in the understanding of statelessness over the last decades. It has been demonstrated that statelessness is not a mere UNHCR ‘Background Note on Discrimination in Nationality Laws and Statelessness’ (20 October 2021), 8 <https://www.refworld.org/docid/616fda104.html>. 90 ibid, 9. 91 ibid, 2. 92 UNHCR, The State of the World’s Refugees 1997-1998 (n 71), 226. 93 Norwegian Refugee Council ‘Statelessness and displacement’ (15 April 2016), 19 <https://files.institutesi.org/stateless_displacement.pdf>. 94 van Waas (n 69), 156-157; UNHCR ‘UNHCR Handbook for the Protection of Women and Girls’ (January 2008), 123-124 <https://www.refworld.org/docid/47cfc2962.html>. 95 van Waas (n 69), 164. 96 ibid, 167-168. 97 ibid, 180-181. 98 ibid, 155-156. 99 ibid, 156. 100 ibid, 170-171. 89 10 Academy of European Law