The objectives of the U.S. government's European Phased Adaptive Approach (EPAA)-the U.S. contribution to NATO missile defense-set out by President Barack Obama in September 2009 were modified over the course of his administration, which ended in January 2017. This study explores how U.S. interactions with Russia and the NATO Allies influenced the decisions on modifications made by the United States-for example, the cancellation in March 2013 of the EPAA's projected fourth phase. This study finds that U.S. interactions with the NATO Allies and Russia played a role in revisions in the original objectives of the EPAA but were not the only contributing factors. Budgetary constraints, technological issues, and reassessments of threats also led to modifications in the EPAA program. Providing for the defense of populations, national territories, and forces remains a high priority for the United States and its NATO Allies, and the Alliance has repeatedly sought dialogue and cooperation with Russia concerning missile defense. Events have vindicated the EPAA's design for adaptability to benefit from technological innovations and to meet the evolving needs for Alliance protection in the international security environment. I. INTRODUCTION * A. MAJOR RESEARCH QUESTION * B. SIGNIFICANCE OF THE RESEARCH QUESTION * C. LITERATURE REVIEW * 1. Obama Administration Policy and Revisions * 2. Ballistic Missile Defense Review * 3. 2010 NATO Lisbon Summit Declaration * 4. Russian Views * 5. Secondary Sources * D. POTENTIAL EXPLANATIONS AND HYPOTHESES * 1. Hypothesis 1: Budget * 2. Hypothesis 2: Technology * 3. Hypothesis 3: Russia's Response * 4. Hypothesis 4: Interactions with NATO Allies * E. RESEARCH DESIGN * F. THESIS OVERVIEW AND CHAPTER OUTLINE * II. HISTORY OF BALLISTIC MISSILE DEFENSE * A. SZILARD LETTER (1939) AND DEVELOPMENT OF THE MANHATTAN PROJECT (1941) * B. BACKGROUND ON BALLISTIC MISSILE DEFENSE (1940s-1960s) * 1. V-2 Rocket, Project Wizard, and Project Thumper * 2. NATO Strategic Concept (1949) * 3. Project Plato and PATRIOT * 4. Nike Zeus, Project Defender, and Nike-X ABM * 5. Reorientation of Missile Defense: Sentinel * C. STRATEGIC ARMS LIMITATION TALKS (SALT) AND ANTI-BALLISTIC (ABM) TREATY * D. PRIORITY SHIFT OF U.S. SECURITY POLICY * 1. Strategic Defense Initiative * 2. GPALS, PAC-3, and THAAD * 3. U.S. Withdrawal from the ABM Treaty and GMD Interceptors * E. BMDR REVIEW OF 2010 * F. LISBON (2010) AND CHICAGO (2012) SUMMIT * G. ORIGINS OF THE EUROPEAN PHASED ADAPTIVE APPROACH * 1. EPAA Phase 1 * 2. EPAA Phase 2 * 3. EPAA Phase 3 * 4. EPAA Phase 4 * H. CONCLUSION * III. NATO RESPONSE TO THE EUROPEAN PHASED ADAPTIVE APPROACH * A. BUDGET CRITIQUE OF THE EPAA * B. TECHNOLOGY CHALLENGES * C. ALLIANCE RESPONSE TO EPAA * 1. Opinion Surveys in Poland and Czech Republic * 2. Polish View on Missile Defense * 3. Canadian View on Missile Defense * 4. Turkish View on Missile Defense * 5. NATO Allies Collective View * D. AMERICAN VIEWS ON MISSILE DEFENSE IN EUROPE * E. ANALYSIS * F. CONCLUSION * IV. RUSSIAN RESPONSES TO U.S. AND ALLIED MISSILE DEFENSE * A. BACKGROUND ON RUSSIAN MISSILE POLICY * B. HISTORY OF RUSSIA, NATO, AND U.S. INTERACTION * 1. Anti-Ballistic Missile (ABM) Treaty * 2. Lisbon Summit (November 2010) * 3. Chicago Summit (May 2012) * 4. NATO-Russia Missile Defense Cooperation Suspended (April 2014) * C. RUSSIAN ARGUMENT ON STRATEGIC DETERRENCE * D. RUSSIAN ARGUMENT ON U.S. GLOBAL AMBITION * E. NATO RESPONSE TO RUSSIA AND JOINT MISSILE DEFENCE * F. U.S. RESPONSE TO COOPERATIVE MISSILE DEFENCE * G. NATO-RUSSIAN JOINT MISSILE DEFENSE CONTRIBUTION * H. ANALYSIS * I. CONCLUSION * V. CONCLUSION * A. SUMMARY * 1. Chapter II * 2. Chapter III * 3. Chapter IV * B. ANALYSIS * 1. NATO Considerations * 2. Russian Considerations * C. RECOMMENDATIONS * D. FINAL REFLECTIONS