Conclusion: The Durability of Liberal International Order - Liberal Leviathan: The Origins, Crisis, and Transformation of the American World Order - page 239

In fact, beyond the navigation of the current crisis, there is reason to think that some type
of updated and reorganized liberal international order will persist. The liberal ascendancy is
not over. This is true for several reasons.
First, the old and traditional mechanism for overturning international order—great-power
war—is no longer likely to occur. Already, the contemporary world has experienced the
longest period of great-power peace in the long history of the state system. 3 This absence of
great-power war is no doubt due to several factors not present in earlier eras, namely nuc-
lear deterrence and the dominance of liberal democracies. Nuclear weapons—and the deter-
rence they generate—give great powers some confidence that they will not be dominated or
invaded by other major states. They make war among major states less rational and therefore
less likely. Nuclear weapons have a double-edged effect. They put limits on the power of
even the most preeminent state in the system. The United States may be unipolar, but it is not
capable of engaging in conquest of other major powers. In this sense, great military powers
of the past may have been less dominant than the United States, defined in terms of share of
material capabilities and military expenditures, but they were nonetheless more threatening to
other major states because the threat of war was real. Nuclear deterrence removes the threat
of war and makes American unipolarity less existentially threatening to other great powers.
At the same time, the removal of great-power war as a tool of overturning international order
tends to reinforce the status quo. The United States was lucky to have emerged as a global
power in the nuclear age, because rival great powers are put at a disadvantage if they seek to
overturn the American-led system. The cost-benefit calculation of rival would-be hegemon-
ic powers is altered in favor of working for change within the system. But, again, the fact
that great-power deterrence also sets limits on the projection of American power presumably
makes the existing international order more tolerable. It removes a type of behavior in the
system—war, invasion, and conquest between great powers—that historically provided the
motive for seeking to overturn order.
The dominance of liberal democracies further reinforces continuity in the system. Chapter
1 provided a depiction of the liberal ascendancy. This is the two-century rise of liberal demo-
cracies to global preeminence. The centrality and sheer bulk of these states creates stability.
If liberal democracies are less likely to go to war against each other, this creates a massive
zone of peace. If liberal democracies are more likely to trade and cooperate with each other,
this reinforces their dominance. If liberal democracies are more able to make political ad-
justments among themselves to accommodate the rise and decline in their power, this, too,
creates more stability in the existing system than in past international orders. Together, nuc-
lear weapons and the dominance of liberal democracies make war less likely as a dynamic
of change. If the violent overturning of international order is removed, the logic of crisis and
change takes a new turn and a bias for continuity is introduced into the system.