At first glance, the new nationalism of conservatives will seem benign and even uncontroversial. In his book “The Case for Nationalism,” Rich Lowry defines nationalism as flowing from a people’s “natural devotion to their home and to their country.” Yoram Hazony, in his book “The Virtue of Nationalism,” also has a rather anodyne definition of nationalism. It means “that the world is governed best when nations agree to cultivate their own traditions, free from interference by other nations.” There is nothing particularly controversial at all about these statements. Defined in these terms, it sounds like little more than simply defending...