Wider and deeper? Enlargement and integration in the European Union

This contribution presents an institutionalist account of the conditions under which widening either impedes or encourages deepening. We argue that the impact of widening on deepening depends on the position of the enlargement state relative to the preference distributions of existing member states. Also, we argue that while expanding to a laggard may in some cases create short-term gridlock, it may also provide the impetus for institutional changes that facilitate deepening over the long-term. We assess our argument empirically drawing on the European Union's own history and data on federal systems and international organizations.