Although President Abraham Lincoln personally hated slavery, his first concern as he contemplated the question of emancipating the slaves during the Civil War was the preservation of the United States. He wrote an open letter in the National Intelligencer newspaper in Washington, DC:

My paramount objective in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone, I would also do that.

Lincoln wanted to free the slaves, but he was concerned about doing it within the constitutional bounds of the presidency. Because of the limits imposed upon him by the constitution, he had to justify the emancipation of slaves as a necessary measure to help ensure the winning of the Civil War. He was also concerned about the reaction of the loyal border states, such as Kentucky, where slavery was still legal.

The First Confiscation Act was an early example of legislation having to do with Confederate slaves. According to this law, any escaped slaves whose labor had contributed to the good of the Confederacy did not have to be returned to their owners. The Second Confiscation Act freed slaves whose owners were proven to be disloyal. As a further measure, the Militia Act authorized the employment of African Americans in the military.

In the meantime, Lincoln had written a preliminary draft of the Emancipation Proclamation. This would officially free all slaves within the Confederacy, a military measure designed to relieve the rebels of slave labor and at the same time increase the ranks of the Union army. Secretary of State William H. Seward counseled Lincoln to wait until the Union achieved a decisive victory in battle before making it public so it would not be perceived as an act of desperation.

On September 17, 1862, the Battle of Antietam, which resulted in a Union victory and Confederate retreat, prompted Lincoln to issue a revised version of the Emancipation Proclamation, which stated that as of January 1, 1863, all slaves in areas designated as rebellious would be forever free.

The pressures were many and they were intense.  The war was well underway by the summer of 1862, and Lincoln was under political  pressure from the abolitionist lobby, which had been united, strengthened and emboldened by the war.  They wanted Lincoln to act decisively towards emancipation.  What was the President worried about, they wondered, offending the South? The pro-slavery Democrats were gone from Congress, seceded along with their countrymen, so many abolitionist northerners lobbied Lincoln for immediate and full emancipation.

Lincoln had strategic interests to consider as well.  The war was going badly for the Union, and emancipation, he worried, might seem an act of desperation, hence his decision to wait until after the Union “victory” at Antietam to issue the Emancipation Proclamation.  He also hoped it would forestall the possibility of cotton-starved Britain's intervention on the side of the South.

Most importantly though, would be the effect the EP would have on the border states, particularly Maryland.  It was already under virtual martial law, and the President had suspended habeus corpus there and ignored the warnings of the Supreme Court in order to do so, which led to his careful wording in the proclamation not to free any slaves in states still loyal to the Union.  The text and timing of the Emancipation Proclamation was, in my opinion, just one example of his political genius.