Answer: D) Westward expansion led to loss of life and territory for Native Americans and added to the growing conflict between "free" and "slave" states before the Civil War.
Explanation: Of the choices offered, the BEST statement regarding the negative consequences of westward expansion in the years before the Civil War is that Westward expansion led to loss of life and territory for Native Americans and added to the growing conflict between "free" and "slave" states before the Civil War.