The concept entered political discourse when, after the end of the Cold War, an eastward enlargement of the European Union began to materialise and the question arose how "widening" could be made compatible with "deepening", i.e., how the imminent enlargement process could be prevented from diluting the idea of an "ever closer union among the peoples of Europe", as the Treaty establishing the European Economic Community of 1957 had put it. In 1994 – still at a time of the
EU12 – the German
Christian Democrats Wolfgang Schäuble and
Karl Lamers published a document in which they called for a
Kerneuropa (= core Europe). This idea envisaged that "core Europe" would have a "centripetal effect", a magnetic attraction for the rest of Europe. A precursor to that concept had been a proposal by two advisors to German Chancellor
Helmut Kohl,
Michael Mertes and Norbert J. Prill, published as early as July 1989. Mertes and Prill called for a
concentric circles Europe, built around a federal core consisting of the
Inner Six (EU6) and like-minded EU member states. In 1994 they partly revoked their original idea, arguing that the post-Cold War EU would rather look like a "Europe of Olympic rings" than a "Europe of concentric circles". The
multi-speed Europe concept has been debated for years in European political circles, as a way to solve some institutional issues. The concept is that the more members there are in the Union, the more difficult it becomes to reach consensus on various topics, and the less likely it is that all would advance at the same pace in various fields. alongside the Outer Seven from 1960 to 1972 Intermediate forms could be limited to some areas of close cooperation, as some historical examples are given below. It is also possible now for a minimum of nine EU member states to use
enhanced co-operation, but this new framework has been used only once. A second proposal, a unified European patent, is nearing completion [as of December 2010] with only two countries (Italy and Spain) not participating. The idea of a multi-speed Europe has been revived because of the following initiatives: • the
eurozone, with 21 member states and one more in
ERM II (
Denmark). Every
EU member except Denmark has agreed by treaty to join, but
many currently have no plans to do so. • the
Schengen Area, with 29 member states, 25 EU members and four non-EU members (
Iceland,
Liechtenstein,
Norway, and
Switzerland). It excludes two EU members:
Cyprus, which is legally obligated to join in the future, and
Ireland, which has an
opt-out from participating. • other initiatives limited to some states, such as the
European Defence initiative and
Prüm Convention. Furthermore, important events were: • the enlargement of the
European Union to 28 member-states and in the forthcoming years other candidates (
Albania,
Bosnia and Herzegovina,
Georgia,
Kosovo,
Moldova,
Montenegro,
North Macedonia,
Serbia,
Turkey,
Ukraine) where new members initially don't join the Schengen area and the Eurozone for some time. • the
European Convention that led to the
European Constitution that was signed in 2004 by the 25 Heads of State, but was not ratified by all national parliaments or assemblies and so failed. Later most of its provisions were adopted through the
Treaty of Lisbon that included additional
opt-outs for some states. • differences of view between EU members on some foreign diplomatic and military issues. In a 2004 article
The Economist compared the variances of Europe to a lake that has many deep parts (areas in which countries are similar) and many shallow parts (areas in which countries have major differences). Currently in the EU there are the following cases of non-uniform application of the
European Union law: == Overview of non-uniformity inside the EU ==