Answer:
He feared that slavery could spread into the free-states.
Explanation:
The Dred Scott decision was a United States Supreme Court case in which a slave demanded his freedom because he had been in two free states before returning back to Missouri. The Supreme Court decision declared that as a slave Dred Scott was not considered a U.S. citizen. As a non-citizen, he had no right to sue in a Federal Court.
Lincoln reacted with disgust to the ruling and publicly speak out against it.
I hope this answer helps you.
