Going through the "On this day" area of Wikipedia, I saw this. What's the story behind taking over 100 years to ratify the 13th amendment? Kentucky didn't do it until 1976.
Edit: I realize unanimity is not a requirement for an amendment to make it's way into the Constitution. But why did Mississippi and Kentucky take so long to ratify it even as a symbolic measure?
Article V of the Constitution governs the ratification of amendments. It requires three-quarters (not 100%) of the states to ratify an amendment in order for it to be adopted. So, by that measure, Kentucky and Mississippi were not necessary for the ratification of the 13th Amendment. Several other states which failed to ratify it before December 1865, when it was officially adopted, did so between 1865 and 1870. Kentucky and Mississippi never got around to it (they explicitly rejected it in 1865). Eventually, they decided to undo the oversight.