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.
While the most common cause of the Civil war is said to be slavery, there were several other factors involved also. Although slavery was the major cause, so to speak, it was definitely not the only cause of the Civil War. As the former led to the latter, abolition of slavery and Civil War have become comparable terms.