Dark Egypt was a term used by Republicans during the Civil War in reference to the southern portions of the states of Ohio ,Indianna, Illinois and Iowa.These areas held the poorer soils of the states and were small farms and towns made up of mostly of illiterate Irish,lowly Germans and ex-southerners.
Illinois Democratic Constitutional Convention of 1862 part of an address by Daniel Rielly,"We believe down in Egypt-in that part of Egypt[seven southern-most Illinois Counties]I have the honor of representing-.."It goes on talking about the railroads and was the start of the Grainger movement. Which is agriculture over industrialism and states rights. I found it interestings as a post awhile back mentioned Little Egypt,IL.

Copperheads in the Middle West,Klement
University of Chicago Press, 1960