The changing structure of European order poses, for any student of international relations, some fundamental questions about the evolution of world politics. Concepts of European order and of the European state system are, after all, central to accepted ideas of international relations. Out of the series of conflicts and negotiations—religious wars, coalitions to resist first the Hapsburg and then the Bourbon attempt at European hegemony—developed ideas and practices which still structure the contemporary global state system: the equality of states; international law as regulating relations among sovereign and equal states; domestic sovereignty as exclusive, without external oversight of the rules of domestic order. The ‘modern’ state system, modern scholars now agree, did not spring fully-clothed from the Treaty of Westphalia at the close of the Thirty Years' War; it evolved through a succession of treaties and conferences, from 1555 to 1714. It remains acceptable, nevertheless, to describe the European state order as built around the Westphalian system.

In the twentieth century, these rules have been modified but not replaced. The European state system—which was the international state system until almost a hundred years ago—has expanded into a global state system. The UN and other global institutions are based upon recognizably similar assumptions to those which governed the eighteenth- and nineteenth-century European orders, modified at the margins to limit the exclusive nature of domestic sovereignty and to give some large states more say in some institutions.