Vol.:(0123456789) International Politics https://doi.org/10.1057/s41311-020-00230-y ORIGINAL ARTICLE Twenty years after: assessing the consequences of enlargement for the NATO military alliance Sara Bjerg Moller 1 © Springer Nature Limited 2020 Abstract How has enlargement afected NATO as a military organization? This arti- cle explores the strategic and military consequences of expansion for NATO as a regional defense alliance. The article makes the case that by pursuing enlargement alongside internal adaptation eforts and by failing to reconcile the tensions resulting from expanding commitments while simultaneously drawing down military forces and shuttering commands, Western leaders’ choices in the 1990s set the stage for many of the strategic problems NATO faces today. Keywords NATO · NATO enlargement · Alliance management · Military planning The decision by Western governments to enlarge NATO following the end of the Cold War represents one of the most consequential developments in the alliance’s 70-year history. Other articles in this special issue investigate the impact that NATO enlargement had on democratic development in Eastern Europe, relations between Russia and the West, and NATO as a political institution. In contrast, this arti- cle explores the strategic and military consequences of expansion for NATO as a regional defense alliance and asks how enlargement has afected NATO as a military organization. In tackling this question, the article looks at the efect that enlargement has had on NATO’s security architecture, conventional military posture, defense planning procedures, budgetary decisions, and operational activities. Understanding how NATO enlargement has shaped the military alliance’s evolution in the past two decades is an important step toward rendering a verdict about the wisdom of post- Cold War enlargement for the alliance as a whole. Any attempt to assess the signifcance of a particular historical event like NATO enlargement inevitably comes with a number of caveats. As noted by others, tack- ling the question of how enlargement afected the alliance from an organizational * Sara Bjerg Moller mollersb@shu.edu 1 School of Diplomacy and International Relations, Seton Hall University, 400 South Orange Ave, South Orange, NJ 07079, USA