Answer:
It ruled against Dred Scott and set aside the Missouri Compromise and popular sovereignty.
Step-by-step explanation:
The case Dred Scott v. Sanford argued whether a slave can obtain his freedom when he step on a state that make slavery illegal.
It happened in 1857. At that time, Dred Scott's (A slave) was taken by his owner from Missouri to Illinois. (According to Missouri compromise, It is still legal to own slaves in Missouri but It is Illegal to do so in Illinois).
Scott tried to make his case to the court stating that as soon as he entered Illinois, his status as a slave should be voided and he should be considered as a citizen.
At that time, The Missouri supreme court ruled against Scott's plead. The court stated that he could never be a citizen since citizenship only apply to white people. So he's still a slave no matter where his slave owner took him.