Final answer:
The 1857 Supreme Court case that ruled Black Americans could not be citizens and unconstitutionalized the Missouri Compromise is Dred Scott v. Sandford, which is often cited as the worst Supreme Court decision and a catalyst of the Civil War.
Step-by-step explanation:
The Supreme Court case in 1857 that ruled Black Americans could not be citizens and declared the Missouri Compromise unconstitutional is known as Dred Scott v. Sandford. This decision, led by Chief Justice Roger Taney, stated that Scott, an enslaved Black man, remained so despite living in free territories. In this case, the Supreme Court held that Black Americans could not be citizens, declared the Missouri Compromise unconstitutional, and also ruled that Congress had no authority to stop or limit the spread of slavery into American territories. This decision played a significant role in exacerbating tensions between the North and South and was considered a catalyst of the Civil War.
Moreover, the Court asserted the broader principle that Black individuals, regardless of slavery status, could not be U.S. citizens. Additionally, it proclaimed that Congress lacked the authority to limit the spread of slavery into American territories, making both the Missouri Compromise and the concept of popular sovereignty unconstitutional. The ruling was a pivotal moment in U.S. history that intensified national divisions and is often referred to as a catalyst for the Civil War. It was later effectively overturned by the Civil Rights Act of 1866 and the Fourteenth Amendment to the Constitution.