This work provides a comprehensive analysis of the key geopolitical events and conflicts that shaped the 20th century, with a particular focus on the Cold War, post-Cold War transitions, and the regional conflicts that followed. Spanning from the ideological struggle between the United States and the Soviet Union to the dissolution of the Soviet Union and the Balkan Wars of the 1990s, this study explores the intricate dynamics of global power shifts, the role of nationalism, ethnic identity, and international intervention, as well as the failure of international institutions to prevent atrocities and conflicts. The study begins with an exploration of the Cold War's defining features, such as the ideological struggle between capitalism and communism, which underpinned global events like the Korean War, the Cuban Missile Crisis, and the Vietnam War. The collapse of the Soviet Union and the fall of the Berlin Wall marked a critical turning point, signaling the end of the Cold War and the beginning of a unipolar world order led by the United States. However, the post-Cold War period was not free from conflict. The Gulf War in 1991 revealed the new world order and the unchallenged military power of the U.S., but it also exposed the complexities of military intervention in the Middle East and the region's instability. The disintegration of Yugoslavia in the 1990s is examined in detail, illustrating the devastating effects of ethnic nationalism, the collapse of communist regimes, and the challenges of international intervention. The wars that followed, particularly in Bosnia and Kosovo, laid bare the weaknesses of international peacekeeping efforts and the moral and political failures of the global community. The Rwandan Genocide of 1994 is another key focus, exposing the catastrophic consequences of international inaction in the face of mass atrocities. Throughout the work, primary sources, historical accounts, and scholarly analyses are used to provide a nuanced understanding of these events. The study emphasizes the lasting impact of the Cold War's ideological and political legacies on global conflicts and examines the broader implications of these events for contemporary international relations, regional stability, and the future of global peacekeeping efforts. The work concludes by highlighting the ongoing challenges in addressing ethnic conflict, genocide, and the limits of international intervention in a world where national interests and global cooperation often collide.