The First World War created the modern world. A conflict of unprecedented ferocity, it abruptly ended the relative peace and prosperity of the Victorian era, unleashing such demons of the twentieth century as mechanized warfare and mass death. It also helped to usher in the ideas that have shaped our times--modernism in the arts, new approaches to psychology and medicine, radical thoughts about economics and society--and in so doing shattered the faith in rationalism and liberalism that had prevailed in Europe since the Enlightenment. With The First World War, John Keegan, one of our most eminent military historians, fulfills a lifelong ambition to write the definitive account of the Great War for our generation.