The paths taken by historians and political scientists intersect less frequently than their subject matter might indicate. Both sets of scholars, for example, have a mutual interest in the formation and evolution of the modern state. However, while this interest has made the ‘Westphalian system’ the common currency of exchanges among political scientists, few historians refer to the concept, and some would not recognize it—even at close range and in full sunlight. Practitioners of the two disciplines often pass like ships in the night because they are unaware of another large presence on a parallel course. In an age of intense specialization we readily become separated, like Alfred Marshall's noncompeting wage groups, from a common body of information. A more formally acceptable justification for discrete enquiries into similar problems lies in the claim that the disciplines have different purposes. The distinction is not, as is still so often said, that historians are interested in the unique and social scientists in the general; it is rather that the analytical issues forming the generalizations that necessarily accompany statements about large issues are of a different order. Political scientists assign significance to the Westphalian system mainly because they wish to generalize about the principles governing the international regime of sovereign states after 1648. Historians, on the other hand, are less interested in testing the merits of realism and its rivals than in charting changing relativities in international relations. Accordingly, they are more likely to set the Westphalian settlement in the context of already evolving state systems and of subsequent changes of equal or greater moment, such as the upheavals caused by the French and American revolutions.