More than sixty years ago Karl Deutsch argued in his seminal work that a ‘security community’ emerges when states agree to resolve their conflicts peacefully, not applying military force against each other but using mostly institutional procedures to overcome their differences (Deutsch, 1957). He pointed out that such states not only exist next to each other, but they also develop trust, shared values, shared identities and a sense of community. Building on Deutsch’s idea, Emanuel Adler and Michael Barnett have highlighted the fact that it is a reasonable assumption in a security community ‘that states do not undertake – indeed, do not consider – security actions that can be interpreted by others within the community as militarily threatening’ (Adler and Barnett, 1998: 34– 5). Adler and Barnett also distinguish between loosely and tightly coupled pluralistic security communities. The most significant difference is that while a loosely coupled security community is only a transnational region where states practise self-restraint based on shared values and identities to ensure ‘dependable expectations of peaceful change’, a tightly coupled security community has become a mutual ‘aid society’ through common institutions and collective security arrangements (Adler and Barnett, 1998: 30– 7). Europe has a tightly coupled security community, which is based on the military, economic and political integration that has happened mostly through NATO and the EU. This is the most relevant precondition that allows the proliferation of multinational defence cooperations (MDCs) in Europe, and the first structural factor discussed in this book.

Before the emergence of the European security community, the danger of war had always loomed over Europe. In the twentieth century, two world wars broke out on the continent, and the Cold War created more than four decades of political, ideological and military divide between Eastern and Western European countries. In previous centuries European states often waged smaller, larger and even Europe-wide wars against each other.

However, now in the twenty-first century it is unimaginable that a war would break out between European countries that are members of the EU and/ or NATO. Accordingly, these states do not perceive any military threats from inside the security community, as they have reasonable assumptions that they will solve their conflicts in a peaceful way mostly through institutionalized processes in the EU and NATO.