Philosopher Bertrand Arthur William Russell (1872-1970) lived almost an entire century, a century full of change. He was one of the few who dared to provide answers to the impossible questions of twentieth century world politics. Several historians have analyzed his attitude towards war, but seldom did they agree on why Russell felt a certain way about war and what caused his often radical attitude. Also, many questions remained unanswered: why did he object to the First World War and supported the Second? And did he really advocate a preventive war against Russia? This book explains the background, motivations and passions behind Russell's sometimes seemingly controversial attitude towards the First World War, the Second World War and the Cold War. By analyzing the consistencies and changes in his thought between 1914 and 1970, the story of twentieth century struggles are relived through the eyes of this invincible rationalist from the nineteenth century.