IT is in the firm conviction that the history of human civilization should be made an object of as scientific a treatment as the history of organic nature that I write this book. Like the phenomena of physical and psychical life, those of social life Should be classified into certain groups, and each group investigated with regard to its origin and development. Only when treated in this way can history lay claim to the rank and honour of a science in the highest sense of the term, as forming an important part of Sociology, the youngest of the principal branches of learning.