America fought its hardest
Answer:
B) Westward Expansion
Explanation:
Manifest Destiny was basically the belief of Americans that it was our right to expand all of the way to the west coast. This eventually helped Americans obtain more land westward and make the 48 out of the 50 states that we have today.
Mainly because it toughened-up the Fugitive Slave Act, allowing official slave-catchers to hunt down runaways.
This recruited many new Abolitionists, and caused Harriet Beecher Stowe to write 'Uncle Tom's Cabin'.
The Virginia Declaration of Rights I believe.