The correct answer to this question is D) Westward expansion.
Westward expansion led to the most sectional strife over slavery in the first half of the 19th century.
When settlers moved to the Western territories during the 19th century, people identified this movement as the westward expansion. It started when the US government reached an agreement with France to purchase the Lousiana territory to fulfill the United States manifested destiny to expand an conquer new territories.
