During the Civil War, with the White Army, later with the Black Sea Navy. Evacuated with the White forces, 1921. Settled in Prague, and taught at the Prague Russian University.
At the end of World War II, in DP camps in West Germany. Taught in schools for Russian refugees. Moved to the USA, 1949.
Professor of Russian history at Yale, Fordham and Columbia universities. Worked in Yale Library, preparing 3 volumes of Russian historical sources, 1957-1972.