Happy Juneteenth! On June 19, 1865, a Union general arrived in Galveston, Texas and delivered a message:
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. The freedmen are advised to remain quietly at their present homes and work for wages. They are informed that they will not be allowed to collect at military posts and that they will not be supported in idleness either there or elsewhere.
Nominally, all the enslaved people in Texas had been free for two and a half years, since the moment when Lincoln made the Emancipation Proclamation. In practice, the Proclamation could only be enforced by Union troops, and it took until the end of the Civil War for enough Union troops to make it all the way down to Texas to enforce the Proclamation.
Maybe you, like me, are struck by the judge-y tone at the end of the Juneteenth order, where recently freed people are urged to continue working for the former masters. It’s worth remembering what the Emancipation Proclamation actually said:
Now, therefore I, Abraham Lincoln, President of the United States, [...] order and declare that all persons held as slaves within [the Southern states, except the parts already under Union control], are, and henceforward shall be free; and that the Executive government of the United States, including the military and naval authorities thereof, will recognize and maintain the freedom of said persons.
And I hereby enjoin upon the people so declared to be free to abstain from all violence, unless in necessary self-defence; and I recommend to them that, in all cases when allowed, they labor faithfully for reasonable wages.
And I further declare and make known, that such persons of suitable condition, will be received into the armed service of the United States to garrison forts, positions, stations, and other places, and to man vessels of all sorts in said service.
Note the curious loophole: the only people nominally freed by the Proclamation were those in places where the Union had no immediate practical capability to free them. This loophole was even noted by members of Lincoln’s Cabinet. Slavery in the United States ended only with the passage of the Thirteenth Amendment, six months after the first Juneteenth. (And even the Thirteenth Amendment allowed “slavery [and] involuntary service [...] as a punishment for crime.”)

Although we now festoon Lincoln with exuberant phrases like “he freed the slaves,” the true historical picture is more complex. Lincoln himself was a moderate abolitionist. In his famous Peoria speech, made in 1864, well into the Civil War, Lincoln takes a position that you might read as either refreshing open-mindedness or as Machiavellian cavil:
Before proceeding, let me say I think I have no prejudice against the Southern people. [...] When southern people tell us they are no more responsible for the origin of slavery, than we; I acknowledge the fact. When it is said that the institution exists; and that it is very difficult to get rid of it, in any satisfactory way, I can understand and appreciate the saying. I surely will not blame them for not doing what I should not know how to do myself. If all earthly power were given me, I should not know what to do, as to the existing institution. My first impulse would be to free all the slaves, and send them to Liberia,---to their own native land. But a moment's reflection would convince me, that whatever of high hope, (as I think there is) there may be in this, in the long run, its sudden execution is impossible. If they were all landed there in a day, they would all perish in the next ten days; and there are not surplus shipping and surplus money enough in the world to carry them there in many times ten days. What then? Free them all, and keep them among us as underlings? Is it quite certain that this betters their condition? I think I would not hold one in slavery, at any rate; yet the point is not clear enough for me to denounce people upon. What next? Free them, and make them politically and socially, our equals? My own feelings will not admit of this; and if mine would, we well know that those of the great mass of white people will not. Whether this feeling accords with justice and sound judgment, is not the sole question, if indeed, it is any part of it. A universal feeling, whether well or ill-founded, can not be safely disregarded. We can not, then, make them equals. It does seem to me that systems of gradual emancipation might be adopted; but for their tardiness in this, I will not undertake to judge our brethren of the south.
To be clear, Lincoln says that, if he could wave a magic wand, he isn’t sure what he would do, and his most likely course of action would be to free the slaves, where “free” emphatically does not mean political and social equality.
Before the start of the Civil War, Frederick Douglass gave a speech about the meaning of “Independence Day.” Douglass, who was enslaved at birth, learned to read and write and eventually planned his escape from slavery by train, disguised as a free sailor. In his speech, he asks:
What, to the American slave, is your 4th of July? I answer: a day that reveals to him, more than all other days in the year, the gross injustice and cruelty to which he is the constant victim. To him, your celebration is a sham; your boasted liberty, an unholy license; your national greatness, swelling vanity; your sounds of rejoicing are empty and heartless; your denunciations of tyrants, brass fronted impudence; your shouts of liberty and equality, hollow mockery; [...]
(You can hear James Earl Jones give the speech.)
For the reasons Douglass laid out, Juneteenth is sometime called the “Other Independence Day,” and thus the holiday’s official name: Juneteenth National Independence Day.