Unionism needs leadership of the kind it had two decades ago which brought the movement into peace talks with Sinn Féin, leading to the Good Friday Agreement, Gerry Adams has said.
DUP leader Arlene Foster should have given her party and followers an ultimatum to "back me or sack me" when she presented draft proposals in the latest round of powersharing talks, the former Sinn Féin leader said ahead of the historic agreement's 20th anniversary.
Speaking about the collapsed talks, which he said he was involved in throughout, Mr Adams said he believed Ms Foster had acted "in good faith" but allowed a unionist "rump" to reject what he described as a good deal.
He said: "What I think she failed to do when she went into her group was 'back me or sack me'.
Northern Ireland's two largest parties were reportedly close to a deal to restore powersharing in February, more than a year after the executive collapsed amid a row over a botched green energy scheme.
But the talks fell apart on Valentine's Day over disagreements about Irish language legislation and there has since been further wrangling between the parties over leaked documents and their content.
Mr Adams said the same people who opposed the latest draft deal were those who ousted Mrs Foster's predecessors Peter Robinson and the late Rev Ian Paisley.
He said: "In their time they got rid of Ian Paisley, they gave Peter Robinson difficulties and then they rejected a draft agreement which ourselves and the DUP leadership had put together just over a month ago."
Mr Adams claimed he told Mrs Foster directly what needed to happen and that unionist leaders privately accept that change is coming on same-sex marriage and Irish language rights - some of the sticking points in political talks.
"And I say that as someone who wants to end the union and who, I believe, we will see the end of the union if we go about it properly."
He declined to reveal what Mrs Foster's response had been, "in fairness to her".
The notion that supporters of the union would be happy for rights around marriage equality and language not to exist in Northern Ireland while being available in other parts of the UK is a "silly contradiction", he said.
Opposition to legislation on such matters will delay rights, rather than stop them, he said, adding that "unionism is on the wrong side of history in relation to all of this".
He urged for similar thinking to that of former UUP leader and first minister David Trimble, a key unionist negotiator in the Good Friday Agreement talks.
Unionist leaders "have to be a wee bit strategic", Mr Adams said.
"The sort of thinking that influenced them to be involved in the Good Friday Agreement in the first instance, the type of thinking which David Trimble and others have explained in their more lucid moments of the fact that the demographics in the north is changing, that there needed to be a new dispensation, in order to protect the union from their point of view.
"That's the sort of thinking that has to start to permeate unionists."
DUP Lagan Valley MP Sir Jeffrey Donaldson dismissed criticism of his party leader.
"Sinn Féin have seen that the DUP is not pushover unionism and that we will hold out until we are convinced that an agreement is right and that it is right for everyone in Northern Ireland.
"The position of the DUP is very clear on this and a position supported right across the party, what was on the table recently was not acceptable to the DUP and it needs to change."