This book uses the agenda of E. H. Carr, and most obviously extends the title of his classic book The Twenty Years’ Crisis, as the point of departure to discuss aspects of the world historical crisis from the end of the First World War until the end of the 1990s. This crisis - identified by 80 years of destructive wars, inequalities in life chances, and today’s casualities of the global political economy - has shaped both the practices of international politics and the way they have been conceptualised and reconceptualised by specialists in International Relations. A distinguished group of contributors have written about the development of the academic discipline of International Relations in the inter-war years, the Cold War and post-Cold War eras; ethics, power and nationalism; the conditions of peace and the roles of law and peaceful change; and finally, considering future prospects, about globalization and the end of the old order.