June 19 marks a special celebration for communities around the United States. Celebrated as Juneteenth, — a combination of “June” and “nineteenth” — the holiday recognizes when the United States ended its historic practice of slavery, legally and in the real world. In this sense, Juneteenth is a day for commemorating the “freedom” of all people living in the United States.

Whether you grew up celebrating Juneteenth or have never heard of it, here’s what you need to know about how the holiday came to be and why it matters to so many people.

How did Juneteenth get started?

President Abraham Lincoln issued the Emancipation Proclamation on January 1, 1863; it was intended, many were told, to free all slaves. But in August 1862, President Lincoln wrote an open letter to Horace Greeley, the editor of the New York Tribune, in which he described his actions as intent to preserve the Union rather than to abolish slavery.

“My paramount object in this struggle is to save the Union, and is not either to save or destroy Slavery,” Lincoln wrote. “If I could save the Union without freeing any slave, I would do it, and if I could save it by freeing all the slaves, I would do it, and if I could save it by freeing some and leaving others alone, I would also do that. What I do about Slavery and the colored race, I do because I believe it helps to save this Union.” Famous for his honesty, Lincoln clearly viewed his decree more as a political tool than a means of liberation.

Its impact bears that out. Lincoln’s 1863 Emancipation Proclamation declared "that all persons held as slaves" within the rebellious states "are, and henceforward shall be free." This meant that the proclamation only applied to states that had seceded from the United States, leaving slavery intact in border states and Southern states under Northern control. In addition, the promise of the abolishment of slavery was contingent on the Union army winning the Civil War, which didn’t happen until April 1865.

But even after that, the Union had to enforce emancipation. In Texas, approximately 250,000 people were still being held in slavery when, on June 19, 1865, Union troops, led by Major General Gordon Granger, arrived in Galveston to announce that the war had ended and that all slaves were now free.

Granger delivered General Order No. 3, which said: “The people of Texas are informed that, in accordance with a proclamation from the Executive of the United States, all slaves are free. This involves an absolute equality of personal rights and rights of property between former masters and slaves, and the connection heretofore existing between them becomes that between employer and hired labor.”

Although slavery wouldn’t legally end in all states until the December 1865 ratification of the 13th Amendment, June 19 — which became known as Juneteenth — was the day when the last American slaves were freed, resulting in massive celebrations.

How do people celebrate Juneteenth?

In 1866, the year after Granger’s order, the first Juneteenth anniversary celebration happened. Since then, celebrations in certain regions of the United States have continued the tradition of honoring this important day. In 1872, a group of former slaves put together $800 and purchased 10 acres of land in Houston, Texas, for the city’s annual Juneteenth celebrations, and they named the space Emancipation Park, where Juneteenth celebrations are held even now. Year after year since, small pockets of the United States have erupted in celebration of the day when everybody in the U.S. was declared free, while the day has gone largely unnoticed in the majority of the country.