When the Cynic philosopher Diogenes of Sinope (c. 412–c. 323 BCE) was asked where he came from, he said "I am a citizen of the world" (Diogenes Laertius, Lives of Eminent Philosophers, bk. 6, chap. 63). The Greek term is "kosmopolitēs," the source of the English word "cosmopolitan." Cosmopolitanism is actually a range of views—moral, political, and cultural—affirming the importance and value of the community of all human beings. Against particular and local allegiance to the polis, city-state, or modern nation-state, the cosmopolitan would emphasize a general and far-reaching concern for humanity.

It remains unclear whether Diogenes' own view was meant to affirm a positive duty to humanity or only to deny the conventional obligations of citizenship associated with the polis. But the Greek Stoics, such as Zeno of Citium and Chrysippus in the third century BCE, developed the tradition by identifying the law of the cosmos with...