I didn’t know that there was another verse of “The Star-Spangled Banner” in which Francis Scott Key crowed that the British could not free American slaves.
" 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.
It seems that the British had offered freedom and land to any slaves in the Americas who fought on their side in the War of 1812. Key was saluting not only the flag still waving supporting slavery.
The British raised six companies of black men who were runaway slaves and resettled them in the Caribbean.
“[T]he British promised refuge to any enslaved Black people who escaped their enslavers, raising fears among White Americans of a large-scale revolt. The final provocation was that men who escaped their bonds of slavery were welcome to join the British Corps of Colonial Marines in exchange for land after their service. As many as 4,000 people, mostly from Virginia and Maryland, escaped.”
That background of 'The Star-Spangled Banner" and its war-like tone is why Congress put off naming it as the national anthem. However, Southern prevailed in giving the song national status.
“The elevation of the banner from popular song to official national anthem was a neo-Confederate political victory, and it was celebrated as such,” Morley wrote. “When supporters threw a victory parade in Baltimore in June 1931, the march was led by a color guard hoisting the Confederate flag.”