The National Liberation Front (FLN) had launched an armed struggle in the North African country in 1954, aiming to end more than a century of French colonial rule.

French historians say half a million civilians and combatants died -- 400,000 of them Algerian -- while the Algerian authorities insist 1.5 million were killed.

Colonial authorities, seeking to boost troop numbers and weaken the FLN, used a mixture of blackmail, violence and financial incentives to persuade what some estimate were 300,000 Algerian Muslims to fight on their side.

After Algeria won independence in 1962, some of the fighters known as "Harkis" moved to France, where they were initially housed in grim camps and have since faced decades of racism.

Others stayed in Algeria, where they are widely seen as traitors.

In both cases, many have left their children in the dark about their role in the war.

- 'Form of protection' -

Harki fathers have often banned their families from talking about the subject "as a form of protection against the shame associated with what they did", said Algerian clinical psychologist Latefa Belarouci.

"Children see the shame of the fathers as a debt," she said.

The quest to reconcile with the past has often been further complicated by the two countries' tumultuous relations since Algerian independence.

Expert Pierre Daum said both France and Algeria have long promoted narratives on the Harkis that are "full of errors".

"The first big mistake is to think that these men joined the French army by ideological choice," he said.

Most had relatives who were starving in French-run "concentration camps", while others, trapped between the FLN and France, had little choice but to join the colonial power, he said.

Daum is just one researcher who is challenging the narrative that after the war, most Harkis moved to France or were massacred in Algeria.

- 'Collective memory' -

Historian Gilles Manceron said it was unclear how many were killed, but that only a small fraction of the Algerian men who fought for France moved there when the war ended.

Those who stayed in Algeria often faced "discrimination or total exclusion", he told AFP.

While many were tortured and some executed for atrocities and alleged crimes during the war, "the vast majority stayed in their villages without being killed", he said.

Anthropologist Giulia Fabbiano said that "the Algerian national discourse still treats (Harkis) as traitors to the nation".

But Harki experiences, both in France and Algeria, were far from uniform, she added.

"Growing up in a Harki family today or in the 1970s in a camp or on the margins of French society" is not the same, she said.

Despite the stigma, "some families in France have kept ties, sometimes very close, with their relatives in Algeria," she said.

And while French presidents since Jacques Chirac have recognised the contribution of the Harkis, psychologist Belarouci said more needed to be done.

Recognition "won't do much to restore their self-confidence, to rebuild their psyche and overcome shame and hatred," she said.

"Only working on the collective memory can do that."