"In the future, Kagan concludes, the U.S. is going to have to stabilize regional conflicts and gradually push back against the autocratic tide. The U.S. will also remain the most ardent champion of liberty in the face of Islamist anti-modernism. American predominance is not a danger. It’s the only thing standing between us and regression to a more dangerous world.
For what it’s worth, I’d say Ikenberry underestimates the power of nationalism. There’s little evidence that different nations with their contradictory moral cultures can really cooperate, except in utter crisis. But I’d also say Kagan underplays postnational threats. More than in the 19th century, security threats come in the form of global guerrillas, loose nukes and disintegrating nations.
Instead, we’re trapped in a hybrid world, in which many problems are postnational but the social structures are unavoidably national. The interesting bright spot is that both Ikenberry and Kagan believe in a Concert of Democracies, an emerging body where countries that do share values can rebut autocracy and consolidate their common success.
It’s a start."