Juneteenth is the oldest known celebration commemorating the ending of slavery in the United States.
A Brief History of Juneteenth
There is a common misconception among Americans that Abraham Lincoln freed the slaves with a stroke of his pen. Yet the Emancipation Proclamation, which went into effect on Jan. 1, 1863, did no such thing — or, at least, it didn't do a very good job of it. Two and a half years later, on June 19, 1865, Union soldiers sailed into Galveston, Texas, announced the end of the Civil War, and read aloud a general order freeing the quarter-million slaves residing in the state. It's likely that none of them had any idea that they had actually been freed more than two years before. It was truly a day of mass emancipation. It has become known as Juneteenth.
Read more - http://content.time.com/time/nation/article/0,8599,1815936,00.html
(Learn more: http://www.juneteenth.com/history.htm )