The Union victory of the Civil War forced the southern states back into the Union under its jurisdiction. On February 1, 1865 President Lincoln signed a resolution permanently outlawing slavery in the U.S. (www.timeanddate.com).
This resolution became the 13th amendment which was ratified later that year after Lincoln's death (www.timeanddate.com).
A former slave named Richard Wright became a successful businessman in Philadelphia in the 1900s (http://www.americaslibrary.gov/es/pa/es_pa_free_1.html). He advocated a day to celebrate freedom (http://www.americaslibrary.gov/es/pa/es_pa_free_1.html). He is considered to have founded the day (Library of Congress Website). In 1948 President Truman proclaimed Feburary 1 to be National Freedom Day (www.timeanddate.com).
You may want to read these books about freedom and slavery in the U.S.:
- The Day Freedom Died: The Colfax Massacre, the Supreme Court, and the Betrayal of Reconstruction by Charles Lane
- Lincoln and the Politics of Slavery: The Other Thirteenth Amendment and the Struggle to Save the Union (Civil War America) by The University of North Carolina Press
- Lincoln and the Thirteenth Amendment (Concise Lincoln Library) by Southern Illinois University Press
- The Promises of Liberty: The History and Contemporary Relevance of the Thirteenth Amendment by Columbia University Press
- The Thirteenth Amendment: Ending Slavery by Enslow Pub Inc
- Who Freed the Slaves?: The Fight over the Thirteenth Amendment by University Of Chicago Press