Like many other historians, the authors of this book believe that there is no single key to understanding the past, and hold that there is no single way in which history should be approached or written. History is the result of the interaction of a multitude of forces. To emphasize some one of these forces may serve to clarify an aspect of the truth; but no simple explanation, no one force, no single school of thought, can offer a complete interpretation of all history. Some factors, however, are more important than others in conditioning the course of world affairs, and the authors believe that the most persistent and fundamental have been the economic factors. In their opinion, it is economic history that serves best the vital purpose of drawing "attention to the enduring and more important actors and scenes in the human drama." - Foreword.