Senior members of Sinn Féin have in recent weeks continued to promote a discredited historical narrative which has also been used by white supremacist groups in the US to attack and denigrate the African-American experience of slavery.

The argument that Irish people were sent as "slaves" to the Caribbean during the Cromwellian era, was deployed again by the party in the wake of the controversy over a racially charged tweet by party president Gerry Adams.

In a radio interview with Ryan Tubridy on RTÉ Radio 1, Mr Adams apologised for his "silly and stupid" mistake on Twitter, but also said he had been "paralleling the experiences of the Irish, not just in recent times but through the penal days when the Irish were sold as slaves, through the Cromwellian period".

Last week Sinn Fein MEP for Northern Ireland Martina Anderson tweeted: "To hell or Connaught To hell or Barbados more Irish sold as slaves to American colonies from 1651 to 1660 than 'free' population of Americas."; and "1641 to 1652 550,000 Irish were killed by England & 300,000 more were sold as slaves. 100,000 Irish kids taken from parents & sold as slaves."

As those words demonstrate, some republicans are intent on drawing direct parallels between the experiences of black people under slavery and of Irish people under British rule. However, in doing so, they are promoting as fact a controversial interpretation of history which goes well beyond academia or Irish politics and spills into the ugly world of racist hate speech.

In the last three years the so-called “Irish slaves” story has become an internet phenomenon, with thousands of online references on blogs, social media and reputable news sites. As Anderson’s tweets indicate, its origins lie in a book called To Hell or Barbados (The ethnic cleansing of Ireland), by Irish writer Sean O’Callaghan, first published by O’Brien Press 16 years ago.

An article in the current issue of History Ireland magazine attacks the "slave myth" applied to indentured servants in Barbados in the 17th century. The authors, Liam Hogan, Laura McAtackney and Matthew C Reilly, argue that the distinction between indentured servitude and slavery is not mere semantic quibbling, given the way in which the "Irish slaves" meme has spread virally across the internet in recent years, and the uses to which it has been put.

Hogan says that O’Callaghan (who is no longer alive) was a well-meaning amateur who misread his sources and greatly overstated the numbers of Irish sent to the Caribbean in the Cromwellian period. Just as importantly, he says, the conflation of African perpetual slavery with indentured servitude, where people were legally required to act as servants for a fixed length of time in often brutal and degrading conditions, is inaccurate and misleading. He also makes the point that this narrative has been used to help obscure the fact that many Irish people participated in and profited from slavery.

Assertions

“The book was published as a piece of popular history,” says Hogan. “Nobody looked at it critically at the time. All the newspapers gave it great reviews.” But in the 16 years since its publication, To Hell or Barbados has been cited many times as showing empirical evidence of Irish slavery. And its assertions have been amplified and exaggerated on Irish and Irish-American bulletin boards and websites. Additional “facts” have been alleged, including that Irish people were treated worse than African slaves, that Irish women were forced to bear children by Africans and that this entire history has been deliberately covered up or hidden.

In the last few years, these claims have been seized on by racist and neo-Nazi websites to bolster their claims of racial superiority. Why is this particular strand of history so attractive to racists? Hogan says it’s because it allows white supremacists to argue that whites overcame a “worse” situation than blacks and that the current socioeconomic position of black people in the US is due to racial inferiority rather than a legacy of historical abuse.

In addition, Irishness has also always been attractive as a badge of white identity to some racists groups. “White supremacists have really jumped on Irish identity as representing a marginalised group which whites can identify with,” he says.

Hogan has documented many instances of the Irish slaves story cropping up in racially-charged situations. For example, at a Confederate flag rally in North Carolina in July 2015, a protester told a reporter for a local paper: “There were more white Irish slaves then there were blacks. And the Irish slaves were treated a lot worse than the black slaves.” At another Confederate flag rally in Mississippi last August, a man approached a Washington Post journalist and said “the Irish were bred with the African slaves, you know? Even the Irish, we were slaves. At some point, you just have to get over it.”

Hogan does not believe Irish politicians are deliberately contributing to this racist historical narrative, but says their refusal to acknowledge the flaws and dangers of the Irish slaves story reflects a broader failure of imagination and understanding.

“Solidarity must include an understanding of the differences between different histories, as well as recognising the commonalities,” he says. “What is lost – if not unconsciously erased – in the defensive reaction to all this is that the system of racialised perpetual hereditary chattel slavery that was developed and enforced by Europeans on African people in the Americas was the most lethal, brutal and genocidal form of slavery that we have ever known, built on dehumanisation and the erasure of identity, its direct legacy is ongoing anti-black racism. I think the overwhelming lack of knowledge about the history of the transatlantic slave trade is a symptom of this and this apathy about the exact details speaks volumes.”