Answer: D. It Coincided With The Harlem Renaissance
Explanation: The Great Migration was the major historical backbone of the Harlem Renaissance. Sure, slavery and the Civil War were important too, because without those two things, people wouldn't have wanted to flee the South in the first place. But in terms of immediate historical relevance, the Great Migration really made the Harlem Renaissance happen. See, during World War I, job opportunities opened up in northern factories. (There's really nothing like a world war to increase employment.) So, African Americans migrated from the South to the North—especially cities like New York City.