The article cited by journalist Radley Balko in the above tweet quotes the rarely sung third stanza of the anthem (see below), noting that the phrase "hireling and slave" refers to black slaves hired to fight on the side of the British during the War of 1812:

And where is that band who so vauntingly swore,
That the havoc of war and the battle’s confusion
A home and a Country should leave us no more?
Their blood has wash’d out their foul footstep’s pollution.
No refuge could save the hireling and slave
From the terror of flight or the gloom of the grave,
And the star-spangled banner in triumph doth wave
O’er the land of the free and the home of the brave.

There are historians (notably Robin Blackburn, author of The Overthrow of Colonial Slavery, 1776-1848, and Alan Taylor, author of "American Blacks in the War of 1812&quot , who have indeed read the stanza as glorying in the Americans' defeat of the Corps of Colonial Marines, one of two units of black slaves recruited between 1808 and 1816 to fight for the British on the promise of gaining their freedom. Like so many of his compatriots, Francis Scott Key, the wealthy American lawyer who wrote "The Star Spangled Banner" in the wake of the Battle of Fort McHenry on 14 September 1814, was a slaveholder who believed blacks to be "a distinct and inferior race of people, which all experience proves to be the greatest evil that afflicts a community." It goes without saying that Key did not have the enslaved black population of America in mind when he penned the words "land of the free." It would be logical to assume, as well, that he might have harbored a special resentment toward African Americans who fought against the United States on behalf of the King.

snip//

The reality is that there were human beings fighting for freedom with incredible bravery during the War of 1812. However, “The Star-Spangled Banner” glorifies America’s “triumph” over them — and then turns that reality completely upside down, transforming their killers into the courageous freedom fighters.

After the U.S. and the British signed a peace treaty at the end of 1814, the U.S. government demanded the return of American “property,” which by that point numbered about 6,000 people. The British refused. Most of the 6,000 eventually settled in Canada, with some going to Trinidad, where their descendants are still known as “Merikins.”

http://www.snopes.com/2016/08/29/star-spangled-banner-and-slavery/