The correct answer is the Missouri Compromise.
The Scott vs. Sandford case was critical to American history, as it stated that slaves are not considered citizens and have no legal rights which white slave owners are bound to respect. Along with this, Scott vs. Sandford also ruled that Congress did not have the power to forbid slavery in any part of the US.
With this in mind, this makes the Missouri Compromise unconstitutional. This is due to the fact that the Missouri Compromise ruled that slavery would be outlawed in all US states north of the 36'30 line.
