Final answer:
President Lincoln's Emancipation Proclamation of 1863 freed slaves in Confederate states in rebellion, while exempting border states and Union-occupied territories. It initiated a shift towards ending slavery, culminating in the Thirteenth Amendment.
Step-by-step explanation:
When President Lincoln issued the Emancipation Proclamation in 1863, he declared that all persons held as slaves within any state or designated part of a state in rebellion against the United States were to be freed. However, it explicitly did not extend to enslaved people in the border states of Maryland, Delaware, Kentucky, and Missouri, or Union-occupied territories like Tennessee and parts of Louisiana and Virginia. These areas were exempt because they were not in rebellion or were under Union control, and Lincoln's authority to issue the proclamation was as commander-in-chief in order to weaken the Confederacy. Considered a strategic war measure, it shifted the war's objectives towards ending slavery.
The Lincoln administration encouraged border states to adopt policies of gradual compensated emancipation. However, Delaware and Kentucky resisted, and Maryland and Missouri experienced political shifts leading to eventual abolition. The Proclamation did not immediately free all enslaved persons, but it was a significant step towards the eventual ratification of the Thirteenth Amendment, which abolished slavery entirely in the United States.