David Olusoga says we British should be more aware of our role in the slave trade. I agree.

For one thing, slavery is not just (just!) a crime against humanity that many would like to forget. Its effects are still with us. Avidit Acharya, Matthew Blackwell and Maya Sen show (pdf) that:

Whites who currently live in Southern counties that had high shares of slaves in 1860 are more likely to identify as a Republican, oppose affirmative action, and express racial resentment and colder feelings toward blacks.

Glenn Loury has written:

The communal experience of the slaves and their descendants [was] shaped by political, social, and economic institutions that, by any measure, must be seen as oppressive. When we look at "underclass culture" in the American cities of today we are seeing a product of that oppressive history.

Graziella Bertocchi shows that states with lots of slaves (pdf) in 1860 have high racial inequality of education today, and because of this have lower incomes. And Robin Einhorn traces Americans' hatred of taxes back to slaveholders.

The impact of slavery, though, isn't confined to the US. Nathan Nunn shows that the slave trade has impoverished Africa today, by reducing trust and political development.

Culture matters for the economy and society. Culture is transmitted from generation to generation. And the culture that sustained slavery, and was produced by it, lingers today. We are creations of our history.

Of course, this is more true of the US and Africa than the UK. But can we really rule out the possibility of a zero impact here?

There's a second reason to be aware of slavery. It teaches us that inequality did not arise from a process of free exchange but rather from the most barbaric practices. Although there's debate about exactly how much the fortunes created by slavery were parlayed into industrial capital and transmitted down the generations to today, it's unlikely that today's inequalities are wholly untainted by that primitive accumulation. As Marx said, capital comes into the world "dripping from head to foot, from every pore, with blood and dirt."

There's something else. The brutality of slavery teaches us that men do not voluntarily exercise self-restraint when pursuing their self-interest. Adam Smith famously wrote that men have a "propensity to truck, barter and exchange." But unlike some of his epigones, he was not so stupid or naïve as to believe that "doux commerce" was our only impulse. He also wrote:

The pride of man makes him love to domineer, and nothing mortifies him so much as to be obliged to condescend to persuade his inferiors*. Wherever the law allows it, and the nature of the work can afford it, therefore, he will generally prefer the service of slaves to that of freemen.

And he'll exploit them to the maximum. In The Great Leveler, Walter Scheidel shows that "early societies tended to be about as unequal as they could possibly be."

This tells us that the obstacles to inequality lie not in the morality of the dominating class but in constraints upon their power. At a time when a serious newspaper can carry a piece applauding the pursuit of "legitimate ethnic interest", this is a lesson that needs repeating.

* I don't know whether we should give Smith the benefit of the doubt and read "inferiors" ironically.