Diogenes the Cynic, asked where he came from, said he was a citizen of the world, a kosmopolitēs. The Stoics developed the idea: all rational beings share in the divine reason and form one city. Marcus Aurelius wrote that his city is Rome, but as a human being, the world.
Cosmopolitanism
Citizenship of the world: the Cynic and Stoic teaching that all human beings belong to one community.
Also: kosmopolites