What makes an ally? Sweden and Finland as NATO’s closest partners

From 2013 onward, Sweden and Finland gradually distinguish themselves from all other NATO partners in order to meet the growing challenge how to defend the Baltics. In the analysis, the concept of ‘informal ally’, in contrast to ‘formal ally’, is introduced. A synthesized analytical framework is used to evaluate the process of ever closer partner cooperation and its shifting focus from cooperative security to collective defense. For NATO, the concept of informal allies is central to address. How do informal allies impact NATO in decision-making, operational planning and crisis response? How can NATO balance in solving its core tasks efficiently, without undermining itself as a multilateral institution? © 2019, The Editor of the Journal.