riddle - separate with a riddle, as grain from chaff screen sift, sieve, strain - separate by passing through a sieve or other straining device to separate out coarser elements; sift the flour
Causing the Civil War. Historically, textbooks have taught that incompatibility between northern and southern economies caused the Civil War. The industrial revolution in the North, during the first few decades of the 19th century, brought about a machine age economy that relied on wage laborers, not slaves.
Causes of secession. The causes of the Civil War were complex and have been controversial since the war began. James C. Bradford wrote that the issue has been further complicated by historical revisionists, who have tried to offer a variety of reasons for the war. Slavery was the central source of escalating political tension in the 1850s.