To all thoughtful persons the European War has brought home with overwhelming power the importance of a knowledge of modern European history. For without such knowledge no one can understand, or begin to understand, the significance of the forces that have made it, the vastness of the issues involved, the nature of what is indisputably one of the gravest crises, if not the very gravest, in the history of mankind. The destinies of every nation in this world and the conditions of life of every individual will inevitably be changed, and may be profoundly changed, by the outcome of this gigantic and portentous conflict.