This article is devoted to the biography of historian Georgii Vernadskii (1887-1973). After publishing several works just prior to wwi, Vernadskii was forced to flee during the civil war to Prague, where, in 1922, he encountered the main theoreticians of Eurasianism, N. S. Troubetzskoy and P. N. Savitskii. However, he soon emigrated to the United States where he became one of the great figures of American Slavic Studies at Yale. His Eurasianist works sought to demonstrate that the history of Eurasia is marked by dialectical rhythms between the Forest and the Steppe, and by the weighty role of geography in Russian history. His later works, less ideological and more historical, are devoted to the history of ancient Russia. They emphasise the interaction between the Slavs and the nomadic Turkic populations, and the major role played by Mongol domination in the formation of the identity of medieval Muscovy.