On June 19, 1865, Union soldiers arrived in Galveston, TX, and they announced that the Civil War had ended and that all slaves were now free.
The Emancipation Proclamation had been signed two and half years earlier, on January 1, 1863. But many states, including Texas, did little to acknowledge President Lincoln's Proclamation until the war ended.
Since 1865, Juneteenth has been celebrated annually on June 19. It is the African American Independence Day.