This book examines the recent changes in strategic stability, caused by the collapse of the international security architecture. Against the background of Russia's invasion of Ukraine, international experts discuss topics and critical issues such as the revanchist strategy of Russia and the readiness of the United States (US) and Europe to give an adequate response; the influence of new technologies in the future of nuclear deterrence; and the crumbling of the arms control and nonproliferation system under the new challenges. The book explains how the combination of these factors lead to a crucial change of strategic stability and the international security landscape, the first such change since the end of the Cold War. Divided into three parts, the book presents timely analyses on (1) US, Russia: New Challenges and Strategic Stability in Europe; (2) Extended Deterrence and Arms Control in Europe; and (3) Regional Dimensions of Strategic Stability in Europe. It further offers perspectives from and case studies on different countries, such as Ukraine, France, Germany, the United Kingdom, the USA, Turkey, Poland, and Romania. This book is a must-read for scholars for international relations, as well as policy-makers interested in a better understanding of the changing international security architecture, Russia's strategy, arms control, nonproliferation, and the future of nuclear deterrence.