D. the Republican Party opposed the Dred Scott decision.
The Dred Scott decision ruled that Dred Scott, a slave, was not a citizen of the United States even though he resided in a free state. It also emphasized that the Congress has no constitutional authority to prohibit slavery in any territory.
The Republican Party opposed this decision because they do not want slavery to expand to federal territories. Because of the ruling, the Republican Party establish a platform that is against slavery expansion beyond the traditional southern boundaries.
The South and the Democrats are pro-slavery.
The North and the Republicans are not.