In the aftermath of World War I, Hungary had to relinquish approximately two-thirds of its former territory and over half of its population under the terms of the Trianon Peace Treaty of 4 June 1920. This inevitably brought about a change in the nationality of persons pertaining to territories transferred to other states. However, the interpretation and implementation of articles concerning nationality were highly ambiguous. For example, the rights of citizenship in a commune, the so-called pertinenza, was not defined in the peace treaty, although the determination of affected persons and beneficiaries of the right of option was explicitly based on that particular criterion. Hence, the fate of these individuals largely depended on the domestic legal regulation and the subjective treaty interpretations of successor states. The application of treaty provisions was not always in conformity with the text, which sometimes proved advantageous, other times disadvantageous for the affected persons. This study seeks to explore the theoretical background, the past and present interpretation, the practical application and the judicial treatment of articles concerning nationality in the Trianon Peace Treaty. The paper also exposes the major problems and shortcomings of the Treaty and makes suggestions for an appropriate wording and adequate interpretation of relevant treaty provisions. Furthermore, in order to provide a full picture of how territorial changes following World War I affected the nationality of millions of individuals, the study takes into consideration other contemporary international instruments with a bearing on the change of nationality or its consequences.

Studies on the relationship between EU citizenship and Member State legal orders speak either of the loss of control over national sovereignty or, on the contrary, the judicial deconstruction of Union citizenship. These firm positions on how EU citizenship should be perceived fit well with the two markedly different mindsets represented in legal literature: while representatives of the federalist view envision a politically integrated, supranational community behind the treaty provisions on EU citizenship, sovereignists oppose the extension of EU powers via judicial interpretation tooth and nail. This study aims to find an answer to the question whether the CJEU, in its latest judgments on EU citizenship issues, has succeeded in consolidating the constitutional basis of EU citizenship in a way that is reassuring for Member States, i.e. by respecting the principle of conferral. In this respect, it may be established that in both cases analyzed below, such as the Delvigne and Tjebbes cases, the CJEU made well-balanced decisions keeping EU as well as Member State interests in mind, which, although has brought no substantial progress in the process of recognizing EU citizenship as an autonomous status, makes efforts to consolidate the fundamental characteristic thereof.