We are now living at a time when the world seems to close inwards rather than opening up toward the outside; populism, narrow-minded nationalism, and racism are on the rise, and right-wing politicians and their parties are gaining ground. The tension between the world’s two largest economies, the United States and China, is aggravated and on a dangerous course. Given the social and political reality of the world today, cosmopolitanism as the ethical principle of treating all human beings as equal is not just morally lofty, but politically necessary for maintaining peace in the world. Immanuel Kant based his argument for cosmopolitanism on the sober-minded recognition of human beings’ “antagonism” and “unsociable sociability,” while the Chinese philosopher Mencius’s argument for an inherently good human nature points to the universal moral principle in all human beings. Bringing the different views of Mencius and Kant as well as Kwame Antony Appiah in a cross-cultural dialogue will contribute to a more comprehensive understanding of the cosmopolitan vision and its importance for our time today.