Answer: A. Missouri Compromise, "popular sovereignty", Dred Scott decision handed down
Step-by-step explanation:
The Missouri Compromise came in 1820 and limited slavery to areas south of the 36°30′ parallel except for Missouri. Popular Soverignity in the form of the Kansas-Nebraska Act repealed this in 1854 and allowed for Kansas and Nebraska to vote on their slavery status.
The widely criticized Dred Scott decision was then passed in 1857 and stated that an enslaved person who had escaped to a free state was still an enslaved person and that African Americans were not citizens.