In The Clash of Civilizations, Samuel Huntington challenged the prevailing consensus that the axes of international geo-political alignments reflect economic and ideological divisions. Based on a top-down analysis of the alignments of nation states, Huntington famously concluded, “The great divisions among humankind and the dominating source of conflict will be cultural.” On the 20th anniversary of the publication of Huntington’s thesis, we revisit his analysis, taking instead a bottom-up view using hundreds of millions of anonymized email and Twitter communications among tens of millions of worldwide users to map the global alignment of interpersonal relations. We also extend previous research on spatial and geographic patterns by examining economic, demographic, historical, political, and cultural correlates of international communication densities. Results confirm the existence of the eight culturally differentiated “civilizations” posited by Huntington, with the divisions corresponding to differences in language, religion, economic development, and geo-location.