Britain outlawed the slave trade in 1807, but its legacy remains. In 2006, Tony Blair, then prime minister, expressed his “deep sorrow” over the slave trade; the Dutch social affairs minister, Lodewijk Asscher, made a similar statement in July.

Britain has already paid compensation over the abolition of the slave trade once — but to slave owners, not their victims. Britain transported more than three million Africans across the Atlantic, and the impact of the trade was vast. Historians estimate that in the Victorian era, between one-fifth and one-sixth of all wealthy Britons derived at least some of their fortunes from the slave economy.

Yet the issue of apologies — let alone reparations — for the actions of long-dead leaders and generals remains a touchy one all over the globe. Turkey refuses to take particular responsibility for the mass deaths of Armenians under the Ottoman Empire, let alone call the event a genocide, as the French Parliament has done. It was not until 1995 that France’s president at the time, Jacques Chirac, apologized for the crimes against the Jews of the Vichy government. The current French president, François Hollande, conceded last year that France’s treatment of Algeria, its former colony, was “brutal and unfair.” But he did not go so far as to apologize.

His predecessor, Nicolas Sarkozy, offered an aid and debt-cancellation package to Haiti in 2010 while acknowledging the “wounds of colonization.”

In Britain, in 1997, Mr. Blair described the potato famine in Ireland in the late 1840s as “something that still causes pain as we reflect on it today,” but suffering pain is not the same thing as making a formal apology.