By 1915, French rule across this stretch of West Africa had become unbearable. The colonial administration seized land, extracted taxes, and treated local custom with contempt. Then came the breaking point. With the First World War bleeding Europe, the governor-general of French West Africa moved to conscript the region's young men into the colonial army, to die in trenches half a world away. For the Marka, Bwa, Bobo, Lela, Nuni and their neighbours, this was a demand too far. The war in Europe had also drawn French strength away from the colonies - and word spread that the occupier was, at last, vulnerable. The coalition that formed was extraordinary precisely because it was not one people or one kingdom but many, villages that set aside old rivalries to face a common enemy.

The numbers tell the imbalance starkly. The rebellion swept in around a thousand villages, home to as many as 900,000 people; at its height the coalition could field 20,000 to 30,000 fighters, and perhaps 130,000 took up arms over the course of the war. Against them the French mustered some 5,000 troops - mostly Senegalese Tirailleurs and local auxiliaries - but those troops carried rifles, six cannon, and four machine-gun units. For a time, fierce resistance and skilled tactics turned back two French suppression campaigns. The villagers knew their ground. They fought on many fronts at once, and they made the colonial army bleed for every advance through country it did not understand.

In the end the cannon told. After roughly a year of heavy fighting, French forces broke the coalition, imprisoning or executing its leaders, while scattered resistance flickered on until 1917. The cost fell, as it almost always did, on the people. The French made no distinction between fighters and civilians, burning about 112 villages to the ground. At least 30,000 Africans were killed - farmers, women, children, the old - against around 300 French dead. These were not statistics to the families who lived through it. They were grandparents and infants, whole communities erased from the floodplain. The exact toll can never be known, because so many of the dead were never counted by anyone who cared to count them.

For all its scale, the Volta-Bani War is barely known outside the region - one of the most significant armed challenges to colonial rule anywhere in Africa, and one of the least told. Yet its mark is permanent. To govern this restive land more tightly, the French carved seven districts out of the colony of Haut-Sénégal-Niger and created a new colony, Upper Volta - the territory that would one day become independent Burkina Faso. The memory survived where official history would not preserve it: in the great novel Crépuscule des temps anciens, written in 1962 by the Bwa author Nazi Boni, son of this country, who turned the uprising of his people into literature so that they would not be forgotten.