Confederate General Robert E. Lee surrendered his army on April 9, 1865, effectively ending the bloody Civil War between the slave-holding South and the North.
But it wasn't until two months later that African American slaves in the Texas town of Galveston were informed that they were free.
That day -- June 19, 1865 -- has been commemorated since then as Juneteenth, also known as Jubilee Day or Freedom Day.
President Abraham Lincoln had actually freed slaves throughout the divided nation two-and-a-half years earlier, with the Emancipation Proclamation issued on January 1, 1863.
But slaves in Galveston did not learn of their freedom until the arrival of Union troops under the command of Major General Gordon Granger.
"The people of Texas are informed that, in accordance with a proclamation form the Executive of the United States, all slaves are free," read an order from Granger.
"This involves an absolute equality of personal rights and rights of property between former masters and slaves," the general's Order No. 3 said.
According to the website Juneteenth.com, the first Juneteenth celebrations were held in Galveston in the years immediately following the war.
In 1872, land was purchased in the Texas city of Houston to celebrate Juneteenth, an area now known as Emancipation Park.
Celebrations of Juneteenth waned in the early 1900s but they experienced a resurgence after the civil rights movement in the 1950s and 1960s.
Juneteenth was made a state holiday in Texas in 1980 and has since been embraced in some form by nearly all 50 US states.
Legislation has been introduced in the US Congress to make it a National Day of Observance and the governors of New York and Virginia -- the one-time capital of the Confederacy -- have moved to make it an official state holiday.
Several major US companies including Nike and Twitter recently announced that they were making Juneteenth a paid holiday for employees.
This year's celebrations will come against a backdrop of nationwide protests for racial justice following the May 25 killing of George Floyd, a 46-year-old black man, by a white police officer in Minneapolis.
President Donald Trump had planned to hold a campaign rally in Tulsa, Oklahoma, on June 19 but he changed the date after a barrage of criticism.
Trump said he did so after "many of my African American friends and supporters" reached out to suggest he change the date "out of respect for this Holiday."
Juneteenth is most often celebrated with backyard cookouts and prayer services but some cities hold parades and other events.
This year's celebrations of Juneteenth will come against a backdrop of protests over the death of George Floyd