Erik Voeten is pleased:

The Realist argument about the importance of the U.S. security umbrella is probably correct. Yet, the dire predictions regarding the future of European integration have yet to materialize. Indeed, the EU sped up its integration considerably with the end of the Cold War; creating deeper institutions and adding fifteen new member states. The integration of the Eastern European former socialist states has not gone without difficulties. Yet, given the scale of the problem, I would argue that it has gone a lot better than it plausible would have without the EU. The promise of EU membership markedly improved democracy, human rights and market economy in all states, although it remains imperfect progress in some. The EU certainly has its share of difficulties, major missteps,  and structural deficiencies. Ultimately, however, my best guess is that Europe is a more peaceful, prosperous, and democratic continent thanks to the EU. A Peace Prize much deserved.

On Facebook, a PhD student at GU sums up the other side of the debate:

Congratulations, Europe. Apparently you get prizes when Germany goes a few decades without invading someone.

Steve Saideman rejects the notion that the EU’s record is that impressive outside of the region.

When the EU has been confronted with a problem of war and peace, people suddenly realize it is a composite of countries with varying interests and commitments and not a single foreign policy-producing entity.  The EU failed its first big test when Yugoslavia fell apart. Its recognition of Slovenia and Croatia did not cause anything really but demonstrated that conditions did not matter more than intra-EU wrangling since Macedonia met the conditions more than Croatia.  The EU split over Iraq 2003, and did not do much more than twitch over Libya.  So, the EU’s record as a force for peace beyond its members is pretty lame.