So why isn't this aspect of the American Revolution better known? Some 19th century historians postulated that people were slaves because they didn't mind being slaves. Incredibly, Harvard scholar John Fiske actually wrote, "The relations between master and slave in Virginia were so pleasant [that the] offer of freedom [by the British] fell upon dull uninterested ears."
Sure. Apparently they missed the former slaves defecting to the other side literally wearing signs that said "Freedom to Slaves."
More plausible, however, is that 19th century abolitionists worried their cause would be hurt if anyone brought attention to the slaves who crossed over to the land of evil accents. They thought it would be better to highlight the courage and sacrifice made by black people -- both slave and free -- in the cause of freedom from the British. As Harriet Beecher Stowe wrote in an introduction to William Cooper Nell's The Colored Patriots of the American Revolution:
"The colored race have been generally considered ... as deficient in energy and courage. Their virtues have been supposed to be principally negative ones. This little collection of interesting incidents, made by a colored man, will redeem the character of the race from this misconception."
That's the gentlest possible reminder that black people died fighting to establish the country that then thanked them by sending them straight back to being slaves.