Brexit has not only destabilized the EU but also research on the EU, especially the theoretical part of EU studies. It is not possible anymore to theorize the EU in focusing exclusively on transnational agency and on the nature of the deals made by transnational agents at the EU level. To understand the future of EU, theorists must mobilize explicitly the variable of domestic politics in their model (political regimes, political parties, social cleavages). Because agents who influence by their political choices the development of EU polity/structure remain mainly national, theoretical modeling must start from the assumption: Domestic Politics influences EU Polity, which in return influences Domestic Politics. It is time for EU scholars to re-invest in a systemic manner the comparative study of domestic politics in the Member States to explain the macro-change in the EU polity. It is also time to abandon the normative term of ‘integration theory’ and to use more the term ‘EU theory’. Brexit shows that the impact of domestic politics on the EU polity does not produce only integration. It can also bring disintegration, another normative term, which cannot be considered equivalent to dilution or dislocation. The EU will survive the exit of the UK, but it will be a different polity, and EU theory will also be different.
