A. A large naval blockade
The North used their navy to prevent ships from leaving the South to trade their cotton with European countries.
The South relied heavily on their trade with Great Britain and France. To cut off the South's economic supply, the North used their navy to block the trade ships. This cut the South off from potential allies in the war and prevented the South from earning money during the war. Eventually the South's trading partners find other sources of cotton hitting the Southern cotton industry even after the war ended.
