“A shared concept of justice,” wrote Henry Kissinger in Diplomacy, is “a prerequisite for international order.” Eighteenth century statesmen understood that. After a decade and a half of constant wars against Napoleon, they crafted the Congress of Vienna.

The great powers went 40 years without warring on one another. The Congress System hung on for another 20 years before collapsing into World War I. The Concert of Europe endured not only because a “balance of power” limited the opportunities for conflict, but also because the domestic populations accepted the arrangement as fair. Power and justice balanced.