This is a very popular idea, but just because something is popular – or even widely believed – doesn’t make it true:
It is not true that tipping is a practice in the U.S. and almost nowhere else. From direct personal experience, having done the job in both countries, it’s possible to point out that tipping is usual in British restaurants (although not pubs) just as it is in the U.S. Which, given that Britain never had domestic slavery – enthusiastic participation in the slave trade, yes, but not chattel slavery within the country after 1066 A.D. – means it cannot be both unique and a legacy of slavery.
To move away from personal experience. Phil Magness – who it should be said disagrees with Nikole Hannah-Jones on many things – has a more detailed refutation here.
Again, from personal experience, different European countries have different attitudes toward tipping and there’s no link to their experience or not of slavery.
Hannah-Jones is making her usual mistake here. Yes, the U.S. experience of slavery was different from that of many other countries. That doesn’t mean that every aspect of American life was determined – or even influenced, by slavery. Sometimes tipping is just tipping.