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: Bleeding Kansas. Proposed by Sen. Stephen Douglas of Illinois, the Kansas-Nebraska Act essentially repealed the line imposed by the Missouri Compromise. Douglas, an ardent believer in grassroots democracy, felt that all the territories should be subject to popular sovereignty.
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.