Those facts weren’t much discussed until the murder of George Floyd, in May 2020, and the global spread of the Black Lives Matter movement. A number of British corporations soon issued public apologies for their connections to the slave trade. A pub chain, Greene King, revealed that its founder, Benjamin Greene, had been given the equivalent of about 500,000 pounds, or $633,000, in today’s money by the British government after the abolition of slavery, to compensate him for losses incurred when he gave up plantations in the West Indies.

“It’s inexcusable that one of our founders profited from slavery and argued against its abolition in the 1800s,” Nick Mackenzie, the Greene King’s chief executive, said in an article in The Telegraph.

That same month, the Bank of England apologized for the “inexcusable connections” involving its former governors and directors to slavery. Lloyd’s of London, the insurance giant, apologized for selling coverage to participants in the slave trade. The company said in a statement, “This was an appalling and shameful period of British history, as well as our own.”

The cascade of apologies was followed by a backlash. It seemed to reach maximum decibel levels in September 2020 when the National Trust, the country’s conservation society, published a list of 93 of its properties with links to slavery and colonialism, including the country home of Winston Churchill. Andrew Roberts, one of Churchill’s biographers, denounced the charity’s “latest excursion into wokery.”

The Guardian’s “Cotton Capital” series provoked glee among the paper’s ideological opponents and had its share of critics, too. Some historians thought the effort was both commendable and a little late. Others praised discoveries like Mr. Taylor’s slave-trade links, but they argued that Manchester’s roots in slavery were well known, making the series feel a bit like a gratuitous smear.