Complex sentence: Robert Palmer believed that after the Civil War, African Americans quickly renewed their long-suppressed percussion traditions: "the passage of the Black Codes, which in most states actually predated the Revolutionary War, did not automatically stamp out all slave drumming".
Split into simpler sentences: Robert Palmer believed that after the Civil War, African Americans quickly renewed their long-suppressed percussion traditions. "To begin with, the passage of the Black Codes, which in most states actually predated the Revolutionary War, did not automatically stamp out all slave drumming".