According to a Wikipedia entry, in 1936, Vladimir Nabokov, then living in Berlin, began seeking a job in the English-speaking world. In 1937, Nabokov left Germany for France. His family followed him to France; they eventually settled in Paris. In May 1940, the Nabokovs fled the advancing German troops to the United States on board the SS Champlain.
In Vladimir Nabokov: The Russian Years by Brian Boyd (Princeton University Press, 2016), pg. 514, it is stated:
By late October 1939 Nabokov had settled arrangements at Stanford [University, to teach a summer course there] with [Stamford faculty member Henry] Lanz. Now ready to apply for a visa, he sought affidavits from eminent Russians in America: the artist Mstislav Dobuzhinsky, the sociologist Pitirim Sorokin, and his friend the historian Mikhail Karpovich, who appears to have put him in touch with Alexandra Tolstoy, the novelist’s daughter. Head of the newly established Tolstoy Foundation, which looked after the interests of Russian émigrés in America, Alexandra Tolstoy secured an affidavit for Nabokov from Sergey Koussevitzky, the longtime conductor of the Boston Symphony Orchestra.
Nabokov became an American citizen in 1945.
All of this is of interest, since Pitirim A. Sorokin had close, extensive contacts with the Russian émigré community. Sergey Koussevitzky was a lifelong friend of Sorokin and his wife Elena.
It would be interesting to know if there exists correspondence between Sorokin and Nabokov.
— posted by Roger W. Smith