Answer:
The harsh climate.
Explanation:
The harsh climate forced some settlers into different areas.
I'm sure the answers d, because it would help way more than the other options you'd want to know first hand what happen the only way to do so is to speak to those who fought in the war.
Manifest Destiny basically mean, "EVERYONE MOVE TO THE WEST NOW!" But with no slaves, how would they create farms to maintain themselves? Easy: expand slavery. However, this was battled against by several sources to create the Compromise of 1850. The compromise delayed the Civil War, despite politicians knowing it will eventually happen. It bought them time-- that was important! Other new states like Nebraska and Kansas were allowed to allow slavery or not. This eventually grew to where the North had no slavery and the South did, which lead to the Civil War.
The Louisiana Purchase, which was purchased by the United States from France, greatly impacted the development of the US in that it gave the US a large area of land for extremely cheap.