The Decline of the West
"The Encyclopedia of Science Fiction" asserts that it was not until the 1950s, and the Okie sequence of stories beginning their run, "did it become clear [Blish] would become a [science fiction] writer of unusual depth". The stories were loosely based on the Okie migration following the Dust Bowl of the 1930s, and were influenced by Oswald Spengler's two-part "Der Untergang des Abendlandes" ("The Decline of the West")"."