The book in your hands, the fourth part of the "International Relations Volumes" series probes into the analysis of the relations between North and South since the formation of this division. The North-South relationship as one product of North-South division is not only the product of contemporary world society, but also a product of relatively gradual historical course closely related with European colonial expansion. The book categorizes European metropolitan states, including the US and Japan, into the scope of the North, while refer to those Asian, African and Latin American colonies and semi-colonies as the South, preferring the terminology and conception of Humanities instead of Economics. Scholars home and abroad understand colonial expansion and the formation and development of the North-South relationship basically in the same way. That is, the world was composed of regions far apart which tended to develop their economies independently till the 16th century. But it was since this period that Europeans cleared away territorial borders, broke through geographical barriers, and unite Asia, Africa, Latin America, some of the Pacific islands, and European countries into a whole by means of their advanced navigation technology, ever-increasing military power, economic power which took shape in this period, and colonial expansion throughout the world. As a result, the former mutually divided world was transformed into a world system dominated by Europe (including the U.S. after the WW II). Scholars home and abroad, however, differ in their view on the formation and development of the North-South relationship within this system. Researchers in Europe and the U.S., from the classical economists in the 19th century to contemporary scholars, believe there exists a mutually beneficial relationship, especially in the economic field, between countries and regions of "the North" which are in the core and their counterparts of "the South" in the periphery within the world system because an open world market benefits both parties. In order to fully discuss and elaborate on colonial expansion and the course of the North-South relationship, we have made new explorations into the style and structure of the whole book. The whole book is divided into two parts. The first part covers chapter I to chapter IV and the second part from chapter V to chapter IX. Part I of the book mainly includes an overall and theoretical description of the process of colonial expansion before the WWII and the development of the North-South relationship. It points out that since the 15th and 16th century with the development of capitalism in Western Europe and the great geographical discovery, colonial expansion has become an important instrument of primitive accumulation of capital by numerous colonial countries of the North, while coercing these countries and regions into an asymmetrical world political and economic system. Part II of the book discusses systematically the development of the North-South relationship after the WW II by tracing the postwar development of international relations. After a relatively clear exposition on some major events and key points in the development process of the North-South relationship, it points out the postwar North-South relationship has undergone a process of dialogue, confrontation, and co-operation and the South-South co-operation after the war plays an increasingly important role in contemporary international relations.