The term 'GRAPES OF WRATH' is a reference to the 1939 novel by John Steinbeck. The novel follows the story of the Joad family, a poor family of Oklahoma farmers who are forced to leave their home due to the Dust Bowl and the Great Depression. The term 'OKIE' is a nickname for people from Oklahoma, and is often used to refer to the migrants who left Oklahoma during this time period. Thus, the crossword solution 'OKIE' is a reference to the Joad family and other migrants in the novel.