Kaya Callas of the EU: Enlargement has been the EU's most successful foreign policy tool for decades. It is not just about enlarging the European Union. It is about making Europe safer and also stronger geopolitically. Ukraine, of course, is Europe's first line of defense against Russian aggression.

Kaya Callas of the EU: Enlargement has been the EU's most successful foreign policy tool for decades. It is not just about enlarging the European Union. It is about making Europe safer and also stronger geopolitically. Ukraine, of course, is Europe's first line of defense against Russian aggression.