Slavery was abolished in the British Empire in the 1830s. As a result, the 1619 Project crowd thinks American independence was actually a step back in the fight for racial justice. If America had remained British, they say, slavery would have ended before 1865. Are they right?
No, because the cost of compensation for slave owners relative to British GDP was very high even without dealing with millions of American slaves. In addition, the British economy was heavily dependent on cheap American cotton, which was, of course, produced by slaves. The politics of the emancipation issue would consequently have been dramatically different if American slavery had been on the table. It is highly likely that Parliament would have decided that it was way too expensive for the British taxpayer.
In short, instead of moving American emancipation forward, a failed American Revolution probably would have delayed emancipation elsewhere.