The Frankfurt sociologist Dieter Prokop believes that the crises of the EU can be better understood when viewed in connection with the institutions and fundamental problems of the EU, and by examining how the crises are interrelated. Prokop's theses: The introduction of the Euro led to the debt crisis, particularly the Greek crisis, which in turn necessitated rescue measures to preserve the Euro. Therefore, one can only understand the bailout fund and the austerity policy if one is aware of the challenges posed by a central currency for states with highly diverse economic, political, and social structures. The austerity policy and the structural reform requirements imposed on Greece have, in turn, resulted in Greece having no means to protect the Schengen external border and allowing illegal entrants to pass through.