To clarify Kimo's statement about Kentucky's status during the U.S. Civil War, it was a "border state." This means that while it never left the Union and was considered Union, it was also a slave state.
The Emancipation Proclamation of 1863 and the reality of slavery still in the border states will eventually force the United States to abolish slavery as Lincoln stated in the Emancipation Proclamation that
Quote:
...all persons held as slaves within any State or designated part of a State, the people whereof shall then be in rebellion against the United States, shall be then, thenceforward, and forever free; and the Executive Government of the United States, including the military and naval authority thereof, will recognize and maintain the freedom of such persons, and will do no act or acts to repress such persons, or any of them, in any efforts they may make for their actual freedom.
This was initially a war measure, designed to disrupt the economy of the Confederate States, but once the United States won the war, slavery ceased to exist in those states "formerly in rebellion."
So what do you do when you have all the non-slave states of the Union and the now slave-free former Confederate states separated by four states where slavery was still legal? I imagine this was a bit of a quagmire for Congress after the war ended.
The end of slavery was not an easy one. The idea of this was first begun formally in Congress in early 1864 and will take until January 1865 to iron out the details. By January 1865, it was becoming clear that the Confederacy was not going to survive the war.
The end result, then, was that the 13th Amendment to the U.S. Constitution was passed on January 31, 1865 and ratified by the states on December 6, 1865 ending slavery in the United States.