I don’t know enough to know the answer to this question, honestly. I know some stuff about the cultural state of slavery at the time of the founding of the US, and how much it already was on thin ice at the time; and that it’s actually very likely that it would have been ended or at least severely restricted by the King of England earlier if the US hadn’t actually won independence (or at least so thought the Southern states). But I don’t realize what was going on elsewhere in the world too, in a way that it would have been abolished there, or not.

What I know: the reason for slavery in the South specifically is that those colonies were funded with much more of a “get rich quick” mentality. Sustainability wasn’t initially the goal, the goal was finding tons of gold and bringing it back to Europe. When the tons of gold didn’t materialize, people had to drastically cut costs to keep those colonies going on other resources; and that’s how, before slavery, indentured servitude was introduced. It initially was a temporary and voluntary state: you’d sign yourself into indentured servitude for a plantation for X years, as a way to pay for your trip to the new world, at the end of which you were free to build the life you want there. Eventually, the plantation owners wondered what it would be like if they didn’t have to set all those people free at the end of the agreement, and obviously it was quite financially successful for them. Eventually, the slave trade and abductions, and all the related horrors, got set up to feed that system.

Anyway, fast forward to the Revolutionary War, and the English crown is showing signs of wanting to regulate that madness. Maybe not abolishing right away, but at least putting serious limits to what people can do. The war starts in the North, with most Southern states not being very interested to join, but what sets the keg on fire was, after the war started, when the King proclaimed that any slave who would escape to join the war effort on the redcoat side would thereby be free. That sent Southerners the message that slavery was on its last leg if the colonies remained English, and is what convinced a number of Southern states to join the rebellion after all.

Eventually, independence is won, but in the 1780s, the King violates the peace treaty of Paris by placing an embargo on America, in order to squeeze them out of money and force them all to join the English empire back (which obviously didn’t quite work!). At the time, the South has most of the remaining funds after a very difficult decade, and little debt (I wonder why!), but if the North goes back to being English, they see the writing on the wall that the South would also eventually be conquered into the English empire again, and therefore slavery would probably end. As a result, the Southern states demand a clause in the US Constitution that forbids the future new US Congress to abolish the Atlantic slave trade (and therefore slavery) at all for 20 years (until 1808). So with that, they have a choice between being sure to keep slavery for at least 20 years, or going back to being English and having it abolished or severely restricted basically any time. That was a key motivator for the Southern states, which tended to be against centralization of government, to still agree to ratify the Constitution.

So to hit it on the nail again: they knew so well that slavery was on its last leg regardless of what they’d do, that they agreed to a very temporary 20-year break to still be sure to stretch it for that time, even if it meant agreeing for the very long-term to something they massively didn’t like the idea of: a federal government. The rest is history.

Anyway, that’s just the US, and even with that knowledge, I don’t know when emancipation here would have occurred if different events had happened; and even less so the rest of the world, of course.