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: Slavery and Control of the Government. Throughout the first half of the 19th century, Southern politicians sought to defend slavery by retaining control of the federal government.
Slavery was the obvious social/political reason for the American Civil War. Most people in the North wanted to abolish slavery, while the Southern society and economy held the institution at its center.