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.
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.