In the early 1850s, with the westward movement, the slavery became a serious political issue endangering the unity of the country because _________. A. whether or not slavery would expand into the future states formed as a result of the westward movement would affect the balance of power in the Senate B. the South insisted that slavery should be allowed to spread into all new territories C. the North refused to let slavery spread into new territories D. the North wanted to put an end to slavery