Final answer:
Abraham Lincoln issued the Emancipation Proclamation to weaken the Confederate war effort and strengthen the Union's moral and diplomatic position. Although it signaled a moral shift, actual emancipation depended largely on the outcome of the Civil War and subsequent legislative actions like the Thirteenth Amendment.
Step-by-step explanation:
Abraham Lincoln believed that freeing the southern slaves would undermine the Confederate war effort by stripping the South of the labor force that supported its economy and military infrastructure. The president based this assumption on the fact that enslaved people working in the fields allowed more southerners to fight against the Union. By issuing the Emancipation Proclamation, which declared the freedom of slaves in the rebellious states, Lincoln aimed to both weaken the Confederate cause and bolster the Union's moral and diplomatic stance, particularly in the eyes of anti-slavery nations like Britain. While it immediately freed few slaves due to the Union's lack of presence in the South, the proclamation set the stage for the eventual abolition of slavery and the formal enlistment of African American soldiers into the Union Army, which strengthened the Union war effort over time.
The Emancipation Proclamation was a critical step towards ending slavery, but its ability to completely accomplish this end was limited by the ongoing conflict and the Union's ability to enforce it in Confederate-controlled territories. The declaration made a significant impact on the war by shifting its purpose from solely preserving the Union to also including the aim of ending slavery.
In conclusion, while Lincoln did possess the power to declare slaves free in the seceded states, the proclamation's effectiveness depended on the outcomes of the Civil War and the passage of the Thirteenth Amendment, which ultimately abolished slavery in all of the United States.