Mississippi has officially ratified the 13th amendment to the US constitution, which abolishes slavery and which was officially noted in the constitution on 6 December 1865. All 50 states have now ratified the amendment.

Mississippi’s tardiness has been put down to an oversight that was only corrected after two academics embarked on research prompted by watching Lincoln, Steven Spielberg’s Oscar-nominated film about president Abraham Lincoln’s efforts to secure the amendment.

Dr Ranjan Batra, a professor in the department of neurobiology and anatomical sciences at the University of Mississippi Medical Center, saw Spielberg’s film and wondered about the implementation of the 13th amendment after the Civil War. He discussed the issue with Ken Sullivan, an anatomical material specialist at UMC, who began to research the matter.

Sullivan, a longtime resident of the Mississippi, remembered that a 1995 move to ratify the 13th amendment had passed the state Senate and House. He tracked down a copy of the bill and learned that its last paragraph required the secretary of state to send a copy to the office of the federal register, to officially sign it into law. That copy was never sent.

Sullivan contacted the current Mississippi secretary of state, Delbert Hosemann, who filed the paperwork for the passage of the bill on 30 January. The bill passed on 7 February. Hosemann said the passage of the bill “was long overdue”.