What marks this century as one of unprecedented upheaval is not primarily the emergence of new centers of power such as China or India; that has happened before, though not on this global scale. Nor is it the fact that significant states are losing control over all or part of their territory. The unique aspect is that when state power weakens, non-state terrorist groups fill the vacuum for the purpose of threatening the state system itself. The challenge is not simply to reestablish an international system but to prevent vacuums that suck into themselves the nihilistic elements trying to destroy order altogether.

At least since Woodrow Wilson, the United States has had its own def-inition of international order: the idea that wars are caused less by clashing interests than by unrepresentative domestic institutions. In the Wilsonian view, foreign policy based on national interest and state power prevails when democratic institutions have failed. Since democracies settle their disputes by reason, not by war, the spreading of democracy is, to this school of thought, America's ultimate mission, and regime change its ultimate sanction.

The belief that compatible domestic structures are the ultimate foundations of international peace is not new. It was the basis of the Holy Alliance after the Napoleonic wars. The opposite of democratic, it asserted that monarchical systems were the best guarantee of international stability because they were impervious to the fickleness of public opinion.