We have grown accustomed in this anxious, post-9/11 era to constructing a world fissured by warring creeds and cultures. Much of humanity now seems separated by chasms of incomprehension. This work challenges the separatist doctrines espoused in books such as Samuel P. Huntington's 'The Clash of Civilizations'. Reviving the ancient philosophy of 'Cosmopolitanism,' a school of thought that dates to the Cynics of the fourth century bce, Appiah traces its influence on the ethical legacies of the Enlightenment, the French Revolution, Kant's dream of a 'league of nations,' and the UN's Universal Declaration of Human Rights. In doing so, Appiah shows how Western intellectuals and leaders, on both the left and the right, have wildly exaggerated the power of difference - and neglected the power of one.