Answer: The 13th amendment, abolishing slavery in the U.S. 

The 13th Amendment to the United States Constitution was passed by the Senate in April 1864, passed by the House of Representatives in January 1865, and  officially adopted and proclaimed enacted in December 1865. This amendment abolished slavery and involuntary servitude. Its first section reads as follows:

Neither slavery nor involuntary servitude, except in the punishment for a crime, whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.

Locally, groups like the Pennsylvania Abolition Society (PAS) had been working for the rights and freedoms of slaves for nearly a hundred years prior. Founded in 1775 at the Rising Sun Tavern in Philadelphia, Society for the “Relief for Free Negroes unlawfully held in Bondage,” the Pennsylvania Abolition Society (PAS) reorganized itself in the 1780s to include the mission of “improving the Condition of the African Race.” For the founders, this primarily meant offering jobs and education to black youth, whether escaped slaves from the South or native Philadelphians. In order to further this part of its mission, in 1790 the PAS appointed 24 members to a Committee for Improving the Condition of the Free Blacks, which was subdivided into a Committee of Inspection, a Committee of Guardians, a Committee of Education, and a Committee of Employ.

HSP has numerous resources on the history of slavery both locally and nationally. The Narrative of the Life of Henry Bibb (Tw. 3737) is a notable example of viewing slavery from the inside out. Other items, such as William Still's Journal C of the Underground Railroad in Philadelphia provide firsthand accounts of slaves' own ordeals during the pre-Civil War days of the 19th century.