The transatlantic alliance (NATO), which has anchored the postwar order for the past century, now faces challenges to its identity, structure, and function alike, as the war in Ukraine continues and the second Trump administration takes office. The administration has brought the long-standing strains of burden, dependence, and trust within NATO into the open, while pushing for a fundamental readjustment of the alliance's identity and role. This agenda is taking shape under the framing of "NATO 3.0." NATO 3.0 goes beyond simple burden-sharing pressure: it is an alliance readjustment that combines political pressure on Europe, adjustments to U.S. force posture, and a reshaping of the command structure. The United States and its European allies broadly agree on the direction of expanding Europe's responsibility for its own defense. They differ, however, on the pace and method of posture adjustments meant to minimize the security gap that could open between U.S. force reductions and European force buildup, and the details remain to be worked out. Amid these shifting alliance dynamics, Europe is pursuing strategic hedging to balance "alliance management" against "strategic autonomy." It seeks to retain a degree of U.S. defense contribution while gradually expanding its own defense capabilities and political and military responsibilities. This is taking concrete form in efforts to strengthen the European Pillar within NATO's collective defense system.

This paper examines the changes now under way in the transatlantic alliance through the lens of NATO 3.0, and highlights the differences between the United States and Europe in how they view and approach the alliance. It assesses Europe's response to NATO 3.0, which has emerged at a time when alliance stability and credibility are weakened, along with the limits of that response, and looks ahead to the strategic choices open to Europe during this readjustment and to the future shape of the alliance. It then considers what these changes and Europe's strategic choices mean for Korea. Finally, it explores the direction and priorities of Korea-Europe and Korea-NATO cooperation amid Europe's changing security environment.​