The book offers a detailed analysis on Russia's invasion of Ukraine. A book needs to be written on this to make sense, from a theoretical perspective, why this invasion has occurred and what the main actors are pursuing. The originality rests on testing main international relations theories: realism, liberalism and constructivism to the war that emerges with the practices and approaches during the Cold War to date from the North Atlantic Treaty Organisation (NATO), the Soviet Union (and now Russia) and Ukraine. The monograph commences with a historical overview of NATO and how it has engaged in expansionism policy to further contain Russia in contemporary international affairs with the accession of additional former Soviet states. This helps to explain the current Russian invasion of Ukraine that would attract great readership. The main argument presented rests on the pursuance of realist interests by NATO, Ukraine and Russia for containment, national security interests and as a response to the security dilemma respectively. This has served as the main catalyst of this conflict that has made diplomacy, international law and collective security measures problematic to implement.