Final answer:
The Emancipation Proclamation freed slaves in Confederate states as Union forces gained control, and while it strategically excluded areas not in rebellion, it became a significant step towards ending slavery and shifting the Civil War's goals.
Step-by-step explanation:
The Emancipation Proclamation freed slaves in areas of rebellion as Union forces won territory. President Lincoln waited for a pivotal Union victory at Antietam before releasing the preliminary Emancipation Proclamation, framing it as a military necessity and a step towards ending slavery.
The final proclamation, effective January 1, 1863, declared that all slaves in rebel states were free, but it pragmatically excluded areas under Union control or not in open rebellion.
This strategic move by Lincoln aimed to punish rebellion, weaken the Confederate resources, and change the objective of the Civil War to include the abolition of slavery. Despite its limitations, the proclamation contributed to freeing many slaves, with nearly 200,000 black soldiers joining the Union army, influencing the war's outcome and paving the way for eventual total abolition.