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
Causes of the Civil War: Abolitionism. The issue of slavery was further heightened by the rise of the Abolitionist movement in the 1820s and 1830s. Beginning in the North, adherents believed that slavery was morally wrong rather than simply a social evil.
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.