An effect of the Supreme Court's ruling in Dred Scott v. Sandford was -

that it caused further separation between the north and south causing the secession of southern states from the Union and the creation of the Confederate States of America.

Explanation:

Americans of African descent, whether free or slave, were not American citizens and could not sue in federal court. The Court also ruled that Congress lacked power to ban slavery in the U. S. territories. This upset the north and south causing the separation.