ppNATO is an alliance transformed. Originally created to confront Soviet aggression, the North Atlantic Treaty Organization evolved in the 1990s as a military alliance with a broader agenda. Whether conducting combat operations in the Balkans or defending Turkey from an Iraqi threat in 2003, NATO continues to face new security challenges on several fronts.pp Although a number of studies have addressed NATO's historic evolution, conceptual changes, and military activities, none has considered the role in this transformation of the secretary general, who is most often seen as a minor player operating under severe political constraints. In iDiplomacy and War at NATOi, Ryan C. Hendrickson examines the first four post-Cold War secretaries general and establishes their roles in moving the alliance toward military action. Drawing on interviews with former NATO ambassadors, alliance military leaders, and senior NATO officials, Hendrickson shows that these leaders played critical roles when mil