I think this bit of news hasn't been emphasized enough, wondering where I should put it, then I noticed your post again, thought it might be a good place:

To add some facts to "what we learned in elementary school... about the late planting".

Supreme Court Justice Joseph P. Bradley, ruled the federal conviction, by jury, of white defendants in the 1873 Colfax Massacre in Louisiana was unconstitutional.  This decision ended federal protection from white terror, murder etc for blacks in the Deep South.

The book, The Day Freedom Died describes the 1873 federal prosecution in New Orleans, convictions by jury, and then the dismissal of the conviction by Bradley, a decision later affirmed the complete Supreme Court.

In a decision that gave free reign to white terrorists the Supreme Court ruled that murder and terrorism is not a federal offense, and that the 14th Amendment to protect civil rights applied only to the actions to deprive rights by state government, not individuals or groups of white terrorists.

14th Amendment:

No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive any person of life, liberty, or property, without due process of law..

Murder and/or lynching, or terror acts like burning down homes or businesses of blacks was not deemed a federal crime in the reconstruction era after 1873. In the unlikely event a state prosecuted such crimes, the terror threats against jurors, prosecutors, and/or white supremacists on a jury would make such action a futile enterprise.

The power of the federal government to prosecute lynching by mobs was still a controversy as late as the 1948 election, as such authority was considered an affront to "state's rights".

I would just like to point out that nobody claimed it was a finished work; rather, this was supposed to be the takeaway:

...It is for us the living, rather, to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced. It is rather for us to be here dedicated to the great task remaining before us -- that from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion -- that we here highly resolve that these dead shall not have died in vain -- that this nation, under God, shall have a new birth of freedom -- and that government of the people, by the people, for the people, shall not perish from the earth

Rough Crossings tells the story of the Black Loyalists who fought with the British

Imagine how history would have unfolded had we lost the Revolutionary War and been brought to heel by His Britannic Majesty, King George III. Instead of being revered as founders, George Washington, Thomas Jefferson and their compatriots could well have been marched to the gallows and forgotten. British propagandists would have churned out a mythology much like the one American schoolchildren are force-fed today — but with the national roles reversed. The British monarchy would be depicted as the champion of liberty, with the rebels cast as agents of republican chaos and tyranny. The lesson would no doubt focus on the contradiction cited by Samuel Johnson, who inquired pithily of the Americans in 1775: "How is it that we hear the loudest yelps for liberty among the drivers of Negroes?" 

Simon Schama's "Rough Crossings: Britain, the Slaves and the American Revolution" picks up where Dr. Johnson left off. It offers a stirringly ambitious reconsideration of the Revolution with the question of slavery set at the very heart of the matter. Schama follows on the heels of historians like Benjamin Quarles, Gary Nash, Sylvia R. Frey and Cassandra Pybus, who have already highlighted the paradox of a revolution initiated in the name of liberty for people who passionately defended slavery. Always a master storyteller, Schama — an Englishman who has long made his home in the United States — has woven the strands laid out by those who went before him into an epic work that gets the reader's blood rushing as it debunks the traditional American view of the Revolution. Schama throws more than a few bombs along the way, as when he writes of the Southern slave owners: "Theirs was a revolution, first and foremost, mobilized to protect slavery." 

"Rough Crossings" focuses on the black American role in the Revolution and, most particularly, on the tens of thousands of slaves who fled to British lines after Lord Dunmore issued a proclamation in November 1775 offering slaves from rebel plantations freedom in return for service to the crown. It was for the most part a nightmare journey. Many runaway slaves were caught by their masters, savagely punished and returned to bondage. Of those who reached British protection, many died agonizing deaths from smallpox and other diseases. Those who survived worked as laborers, guides, spies and fighters. They often served valiantly — at one point wearing sashes that read "Liberty to Negroes" — and spilled the blood of their former masters with alacrity. If nothing else, Schama's portraits of black loyalist fighters should provide Hollywood with fresh ideas about how to depict this war. Screenwriters will find prime material, for example, in the black guerrilla fighter known as Colonel Tye, who escaped from his master in New Jersey, survived the epidemics that ravaged Dunmore's Ethiopian Regiment in the Chesapeake and returned North to haunt the patriot outposts that were reachable from the British stronghold of New York.

https://www.nytimes.com/2006/06/04/books/review/04staples.html