What document did Abraham Lincoln issue to free the slaves in Confederate states?

The Emancipation Proclamation is the correct answer because it was a pivotal executive order issued by President Abraham Lincoln on January 1, 1863. This proclamation declared that all slaves in the Confederate states were to be set free. It was a significant turning point in the Civil War, as Lincoln aimed to weaken the Confederacy and encouraged enslaved individuals to escape or rise up against their masters.

The proclamation did not immediately free all slaves, particularly in border states that remained with the Union, but it symbolized a shift in the war's purpose from simply preserving the Union to also addressing the issue of slavery. This move was intended to bolster the Union's moral cause and was a critical step toward the eventual abolition of slavery in the United States, which was formalized with the passage of the Thirteenth Amendment in 1865.