Answer:
Abraham Lincoln and Stephen A. Douglas disagreed on whether slavery should be allowed in the states where voters supported it.
Step-by-step explanation:
While both Lincoln and Douglas wanted to contain the spread of slavery westwards, they had different perspectives on how to achieve it. Douglas wanted popular sovereignty and people to vote against slavery on each state. However, the Supreme Court's Dred Scott decision proved his approach was useless.
On the other hand, Lincoln wanted to outrun the Dred Scott decision and forbid slavery in the territories under federal rule.