Russia's seizure of Crimea in the Ukraine rung alarm bells in the West, raising fears of a resurgent Russia intent on regaining its former dominance in Eastern Europe. Over the last two years, the North Atlantic Treaty Organization (NATO) has renewed its focus on defending its member nations from an aggressive and resurgent Russia. This focus encompasses a switch from assurance, which the United States and NATO have relied on during the post-Cold War era, to deterrence which is more in line with its posture against the former Soviet Union. NATO was created in 1949 as part of a broader effort to serve three purposes: deterring Soviet expansionism, forbidding the revival of nationalist militarism in Europe through a strong North American presence on the continent, and encouraging European political integration. During the Cold War, NATO pursued deterrence by both punishment and denial. Deterrence by punishment sent a message based on 'unactable damages', which included a threat of massive nuclear retaliation for any Soviet attack - conventional or nuclear. Through deterrence by denial, NATO deployed a forward defense at its eastern border with the Soviet Union in order to make it physically difficult for the communist nation to achieve its expansionist objective.This compilation includes a reproduction of the 2019 Worldwide Threat Assessment of the U.S. Intelligence Community.After the fall of the Soviet Union, NATO's deterrence posture deteriorated as the world view shifted. Its forces, conventional and nuclear, were dramatically downsized and nation members consistently reduced their defense spending contributions. Additionally, NATO experienced an atrophy of deterrence know-how, including planning, exercises, messaging and decision making. This is because NATO's post-Cold War security environment changed. NATO became more involved in crises like the western Balkans and Afghanistan. Following the Cold War, NATO no longer considered Russia an adversary and some of the former states have since become members of the alliance. As a result, the size of NATO's military presence has been significantly reduced over the years. There may also be a question of the commitment of some of its members when it comes to monetary contributions. Each nation is expected to expend the equivalent of two percent of its gross domestic product (GDP) in support of NATO.9 However, many nations fall very short of that number. In fact, of the 28 countries in the alliance, only five-the U.S., Greece, Poland, Estonia and the U.K.-meet the target.