Final answer:
Lincoln sought to keep Delaware, Kentucky, Maryland, and Missouri, known as the border states, in the Union by promoting gradual emancipation, in light of their strategic importance to the Civil War.
Step-by-step explanation:
President Abraham Lincoln was very concerned with trying to prevent the border states of Delaware, Kentucky, Maryland, and Missouri from seceding during the American Civil War. These states were crucial due to their natural and industrial resources which would significantly increase the Confederate military manpower and manufacturing capacity, profoundly impacting the conflict. Lincoln encouraged policies of gradual compensated emancipation in these states as a model for the nation, with the hope that this would keep them loyal to the Union. Delaware and Kentucky resisted the pressure, while Maryland and Missouri underwent significant political changes, increasing political power for whites previously excluded and leading toward emancipation support, partly because of the presence of federal troops. Lincoln's concern extended to balancing the needs of slaveholders with freedom for refugees, leading to the Confiscation Acts and eventually to the Emancipation Proclamation as part of his policy for reunifying the nation.