The Treaty of Paris created 13 new countries!
Each one of these independent states had the prerogative of continuing in place the slavery previously imposed on the inhabitants by foreign nations who claimed OWNERSHIP of everybody and everything there.
Or, they could get rid of it.
Or they could waffle.
Massachusetts followed a path of dwadling and misadventure, but ended up discovering they'd abolished slavery earlier only no one noticed: http://www.slavenorth.com/massemancip.htm
Pennsylvania abolished slavery the day the proprietor Penn took over (theoretically). Then, they reacquired it following a line of argument that said it'd never really been abolished properly. By the time of the Revolution there was a well established body of abolitionists in Pennsylvania ready to argue in court, or whenever, on behalf of slaves who wanted loose.
All the other slave-holding Northern States had a similar back and forth ~ for one thing, there was not much economic interest in slavery in the North. Plus, you add to that the decided distaste for slavery engendered in the white population by the Swedes who kidnapped people and transported them toAmerica, as well as limited indenture to pay for transport to America to farm, slavery would never be popular in Pennsylvania!
In the early period after the Treaty of Paris the folks acting in regard to the continuation of slavery were ALL FOUNDERS. They managed to get rid of it IN THE NORTH, and in most of Virginia's Western land claims.
The Virginia trick was first to have Virginia and all other states "donate" or "yield" their colonial era land claims to the federal government (under the Articles of Confederation). Then, when that vast territory was subjected to organization for settlement the next trick was to simply prohibit slavery in any new territory. This affected portions of what are now New York, Pennsylvania, and all of Ohio, Indiana, Illinois, Michigan, Wisconsin, and portions of Minnesota right up to the Spanish boundary.
The fellows who created the Old Northwest as Free Territory were, of course, among the Founders.
There was less success in the Souf' where slavery had economic advantage.
Leastwise, that's the way I recall it.
Now, going back to that Swedish thing ~ most people are unaware that the early settlers at the New Sweden colony in Delaware were actually put to work in what is now Maryland cutting down trees for the Swedish and British navies.
For the most part those earliest settlers were acquired through the simple expedient of kidnapping entire families of Sa'ami who ventured too far South in the winter. They'd then be transported to America, turned loose, and put to work.
The Finns usually claim these Sa'ami were Finns, but the Sa'ami know better. Numerous family journals reflect their travel from the unpaid treecutting slavery of Maryland to liberty up the Susquehanna in Pennsylvania and New York.
I think most of that slavery was ended as the Sa'ami acquired firearms. No doubt folks like to imagine this never happened but it did.
You know those ol'boys down there at Valley Forge without shoes in winter? Those are the Sa'ami in the 2nd Pennsylvania. And the guys who are out there digging George Washington across the frozen Delaware in a boat to attack the Hessians? Those guys are Sa'ami too.
George would go nowhere without his Marylanders and his Pennsylvanians. The Maryland 400 had, in fact, saved the Army and the Revolution earlier in the withdrawal from New York. This was, by that time wholly their country. Let me assure you most of those guy's Great Grandfathers weren't too clear about where they'd come from but this piece of America was theirs ~ end of the line ~ no more choices ~ and the Brits didn't have a chance.
Ultimately neither did slavery.