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.
The salient cause of the Civil War was the conflict between slave and free states over the future of slavery in the United States. The conflict was kept from boiling over in the early decades of the 19th century because of political compromises and a rough equivalence between the numbers of slave and free states.