I remember reading something that said during the Revolutionary War the British offered freedom to Southern slaves who joined their side.
Yes, this is true. After the patriots started putting in abolitionist efforts it became a wedge issue used by both sides to hurt the other side.
The colonies passed the Continental Association(1774), which completely banned all slave trading.
This was designed to hurt Britain economically.
Conversely, the British had Dunmore’s Proclamation. This was designed to hurt the patriots militarily.
The hills of the Appalachian frountier contained a ready force of Scots-Irish indian fighters, brought there by the crown to quiet the frontier for colonization. They were seasoned and their loyalty was to the livelihood scatched from the good land around them. Any threat from any quarter, was not welcome.
Dunmore’s Proclamation of 1775 offered freedom to any slave who fought for the Royal government.
The Philipsburg Proclamation of 1779 went even farther, offering freedom to any and all slaves.
Had the Royal government defeated the rebels and traitors of 1776 then slavery in America would have ended some 80 years sooner.
https://blackloyalist.com/?page_id=631