One day in 1998, David Diop came across a published collection of letters written by French soldiers in first world war. “That was the point of departure: 23 years ago,” he laughs. That reading culminated in 2018 in his second novel Frère d’âme (“soul brother”). It had already raked in several awards before the English translation, At Night All Blood Is Black, won the International Booker Prize last week.

“Reading those letters,” Diop recalls, with the gentle didacticism of the university lecturer, when we speak via Zoom, “I was really extremely moved. Maybe the violence in Frère d’âme I owe to the violence of the testimonies in those letters.”

However, all the letters in the collection were from white French soldiers. Diop knew about the 200,000 or so “tirailleurs sénégalais” — literally, “Senegalese riflemen”, though in fact recruited from across all French colonies in west Africa — who fought for France in the first world war. He recalls from his school years in Senegal that the last survivors had to subsist on pensions of €5 a month.

Had the riflemen, many of whom wrote excellent French, left any wartime letters? “There are some,” Diop says, “but they are impersonal, administrative, and there was censorship.” Craving a personal west African testimony of the trenches, he decided to write a fictional one. Now it has plunged him, somewhat reluctantly, into the international debate about silenced black voices and the reckoning with colonialism.

Diop is both a French writer and an African one. Born to a Senegalese father and a white French mother in 1966, he grew up between Paris and Dakar, and became a literary scholar at the University of Pau in southwestern France, specialising in European depictions of Africa and Africans during the Enlightenment. His little-noticed first novel 1889, l’Attraction universelle, published in 2012 and not yet translated into English, is about a Senegalese delegation that travels to France for the 1889 World Fair in Paris but gets stranded in a circus where Africans are exhibited as freaks to Europeans.

The author’s fascination with the first world war came from his French side too: his mother’s grandfather had fought in the trenches, but could never talk about it afterwards.

At Night All Blood Is Black tells the story of one Senegalese rifleman, Alfa Ndiaye. After watching his “more than brother” from his native village die horribly, Alfa turns into the “African savage” that his French comrades expect him to be. He ritually disembowels German soldiers in one-on-one encounters, then carries back their amputated hands to the French trenches. His commander complains that his methods are “a bit too savage”, and not in line with the “civilised war” of mass mechanical slaughter. In the second half of the novella, we learn about Alfa’s African origins.

The story is narrated by Alfa in classical French — with the oddity that the character himself speaks not French, but the west African language Wolof, spoken mostly in Senegal, Gambia and Mauretania. Diop says: “I gave the French a different rhythm, to suggest that behind this French there is Wolof. I reproduce its rhythm by repeating certain phrases.” Alfa keeps using the phrases, “God’s truth”, and “I know, I understand”.

Diop’s translator into English, the American poet Anna Moschovakis, saw her job as “translating a translation (my translation of the author’s translation of the character’s thoughts)”. Diop has read only fragments of the English text, but he has listened to the English audiobook, read by Dion Graham. “I understood that Anna Moschovakis did a superb translation when I heard the text’s rhythm, which coincides perfectly with the rhythm in French”, he says. (They both shared the International Booker prize and the £50,000 prize money equally.) He hopes someone will now translate his novel into Wolof.

The award comes at a moment when European-African encounters are headline news. After last year’s global Black Lives Matter protests and toppling of slavers’ statues, Emmanuel Macron has just admitted France’s role in the 1994 Rwandan genocide, while Germany has recognised its genocide of Namibians from 1904 to 1908.

The world, it appears, is catching up with the themes that Diop had been quietly studying for 15 years. “Through my academic work I have been asking these questions for a long time,” he says. “This is an old current of historians and social scientists who work on forgotten voices or stifled voices, because history is obviously written by the winners.”

He adds: “If the book enters the political debate, that doesn’t bother me. But I don’t want to say anything more than I have written. I am a man of writing. Readers must make what they want of the book. I don’t feel the need to add a verbal layer to it.”

Diop’s novel has been especially well received in west Africa. “For readers in Senegal, there is the pleasure of finding a familiar cultural horizon in a novel,” he says. “Our shared cultural references allow them to use other keys to understand the main character’s state of mind.”

Then there is the “historical vision” of things. “It pleased Senegalese readers to see the memory of the riflemen restored. These people gave their blood for the motherland, for France. And there was a period of resentment, because the promises made to them were not kept”.

But Diop has been struck more by the similarity than by the differences in readers’ responses around the world. He has found that despite Alfa’s monstrous deeds, most readers feel compassion for him. He thinks that is because the character is more than just a representative victim of colonial brutality and war.

“When the historians I’ve read speak of the Senegalese riflemen, they see them together. That’s the work of an historian: to create groupings, and to say, ‘Voilà, this many riflemen came from that place, which means that in that region France had more weight and more efficient recruitment commissars.’ Historians see the great ensembles,” says Diop. “What interests me — and that’s what literature permits — is to apprehend characters in their singularity. And it’s this singularity that is their humanity. Alfa has a unique interiority, and isn’t simply an indistinct member of a large group. That’s what prejudice is: it erases distinctions.”

Diop’s next novel, La Porte du voyage sans retour, out in French in August, is about the 18th-century French botanist Michel Adanson, who travelled to Senegal. It is another version of Alfa’s journey, and of the author’s own.

Simon Kuper is an FT columnist

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