By the standards of prosperity and peace, the post–Cold War international order has been an unparalleled success. Over the last thirty years, there has been more creation of wealth and a greater reduction of poverty, disease, and food insecurity than in all of previous history. During the same period, the numbers and lethality of wars have decreased. These facts have not deterred an alternative assessment that civil violence, terrorism, failed states, and numbers of refugees are at unprecedentedly high levels. But there is no global crisis of failed states and endemic civil war, no global crisis of refugees and migration, and no global crisis of disorder. Instead, what we have seen is a particular historical crisis unfold in the greater Middle East, which has collapsed order within that region and has fed the biggest threat to international order: populism in the United States and Europe.
Civil wars and their relationship to international order differ dramatically by historical era. In the first half of the nineteenth century, the great powers treated national rebellions as threats to international order and sometimes cooperated in suppressing them. During the Cold War, the superpowers viewed civil wars as proxy competitions, and armed and financed client governments or rebels in order to prevent them from losing. The post–Cold War order, by contrast, devoted substantial effort to the treatment, mitigation, and resolution of civil wars, usually with the cooperation and consent of great powers. At the same time, those same great powers were often unable to reach agreement on when and how military force should be used for humanitarian purposes in civil wars.
The effects of civil wars on international orders also differ across historical eras. Civil wars may be fought over principles that undermine the norms and rules that undergird an international order. Civil wars may tempt intervention by great powers . . .