The collapse of communism, symbolized by the fall of the Berlin Wall in 1989, made it possible to expand the EU to the East. This expansion was immediately perceived as a great opportunity to extend European integration to Central and Eastern Europe. As the European Union (EU) Commission aptly put it,

The economic impact of enlargement will be significant, as a bigger and more integrated market boosts economic growth for new and old members alike. The newcomers stand to benefit from investments from firms based in western Europe and from access to EU funding for their regional and social development. Integration of their economies with the rest of the EU is already under way, as trade agreements, negotiated and applied in advance of membership, have already removed virtually all tariff and quota barriers on their exports to current member states.

Policy harmonization deepens the cooperation within the Union but the widening of the EU is the second pillar of EU integration. Consequently, explaining the conditions under which enlargement succeeds contributes not only to our understanding of the enlargement process itself but to our understanding of EU integration in general. Given how important such understanding is and how beneficial EU members and candidates alike have perceived integration to be, it is indeed astonishing how little we still know about the enlargement process itself.