Answer:
Abraham Lincoln and Stephen Douglas held differing views on the expansion of slavery in the United States. Lincoln, in his famous 1858 "House Divided" speech and later during the Lincoln-Douglas debates, argued that the nation could not continue to exist half slave and half free. He believed that allowing the expansion of slavery into new territories would ultimately lead to the degradation and eventual demise of the Union. Lincoln's argument was grounded in the idea that a nation divided against itself on such a fundamental moral issue could not endure.
On the other hand, Stephen Douglas, while not necessarily advocating for the spread of slavery, believed in the principle of popular sovereignty, which allowed settlers in a territory to decide by popular vote whether or not to allow slavery. Douglas contended that this approach could maintain the Union, as it allowed states to determine their own institutions without interference from the federal government. He saw this as a way to uphold the Union while avoiding conflict over the issue of slavery.
In summary, Lincoln believed the nation could not endure as a house divided over the issue of slavery, while Douglas believed that the principle of popular sovereignty could allow for a peaceful coexistence of slave and free states. Their differing views on this pivotal issue contributed significantly to the lead-up and context of the American Civil War.