Four years of residence in the Ottoman Empire, chiefly in Constantinople, during the most disastrous period of its decline, have led me to investigate its origin. This book is written because I feel that the result of my research brings a new point of view to the student of the twentieth-century problems of the Near East, as well as to those who are interested in fourteenth-century Europe. If we study the past, it is to understand the present and to prepare for the future.