Schmid Comparative Migration Studies (2020) 8:25 40). If access to citizenship were completely blocked, immigrants could never become equals. In addition, the transformation of non-citizens into citizens has crucial repercussions on territorial admission: It permanently unlocks access to a state’s territory by establishing the right of unconditional re-entry and residence. The outer boundary of immigration is also fundamental. If it were completely blocked, citizenship could never be reached. Indeed, the territorial boundary is ‘citizenship’s perpetual gatekeeper’ (Joppke 2010, p. 150). Immigrant rights are important, but not as fundamental as immigration policies and citizenship policies. Still, one may argue that the architecture of national boundary regimes cannot be properly conceptualised and understood without the dimension of immigrant rights. However, there are empirical, theoretical, and pragmatic reasons to omit this dimension. First, Huddleston and Vink (2015) provide empirical evidence showing that various general rights and the ease of access to citizenship are so highly correlated that they can be reduced to the same empirical dimension. They identify the citizenship policy component as the ‘best predictor’ of the overall rights regime. Second, granting rights amounts to boundary blurring between citizens and non-citizen residents, while the establishment of long-term legal residence upon immigration and the inclusion into a receiving country’s national community regulate the more fundamental aspect of boundary crossing. Lastly, comprehensive data on immigrant rights for the sample and timeframe used in this study are not available, especially for the last decades of the old millennium. Such data would be very laborious to collect, especially when one considers a wide variety of rights. To make such an endeavour possible we would also have to narrow the number of rights we examine, provoking the need for a selection that can be widely agreed upon. For these reasons, I leave aside immigrant rights and focus instead on the fundamental boundaries defined by IRO and CRI. Theorizing the architecture of national boundary regimes To theorize the architecture of national boundary regimes, I first take a step back and examine the idea of the liberal paradox. Coined and elaborated by Hollifield (1992, 2004), it refers to the tension between economic liberalism and political liberalism in regulating immigration and the access to citizenship. To maximize material welfare in a globalizing world, transnational economic forces propel liberal states toward greater openness in territorial admission (Hollifield 2004, p. 902). At the same time, however, to ensure security, to preserve the democratic social contract, and to protect the cultural cohesion of the national community, political forces push for greater territorial closure (ibid.). Furthermore, however, whereas economic liberalism tends to see foreign workers as commodities, the liberal constitutional order of democracies provides the grounds for granting them rights and citizenship (Hollifield 1992). Against this background, Hollifield points to two possible outcomes. The first is that – in the context of a growing international labour market – an individualist understanding of political liberalism points to the possibility of a “gradual resolution of the liberal paradox” (Hollifield 1992, p. 223). Indeed, for Hollifield, “rights-based liberalism goes hand-in-hand with the spread of market relations”, and it is this “confluence of unregulated markets for foreign labour and the rise of rights-based politics that explains the failure of restrictionist policies and the persistence of immigration” (ibid., p. Page 5 of 20