ABSTRACT
Wars and crises are often seen to be transitions between one type of international system and another, or a turning-point or watershed in relations between states. But often this can be determined only in retrospect. The two world wars of the twentieth century were very large-scale events involving the great powers of their respective times, and the changes that followed them were profound for the whole international system, representing in both cases a change between one age and another; or perhaps as two ‘stepped’ changes that brought the modern world into existence. There is not scope here for a lengthy discussion on the subject of whether these wars were in a sense the midwives of those profound systemic changes or indeed themselves a manifestation of those changes-suffice it to say that the causal relationship between these phenomena will not be simple or straightfoward.
