DUP was spooked into engineering changes in the North
As we know the Assembly was disestablished in the North by the withdrawal of Sinn Féin. This situation was engineered by the DUP by the refusal of its leader to stand down during the investigation of the cash-for-ash controversy and the unwillingness of the DUP to legislate a very inexpensive Irish language bill, both of which left Sinn Féin no option but to resign to protect its credibility with the electorate.
The reason behind the DUP's action to engineer a situation that would inevitably lead to the collapse of the Assembly were the utterances by Micheál Martin and Leo Varadkar that, as a result of Brexit, the prospect of a united Ireland was brought nearer. This kind of language was normally associated with Sinn Féin but when the leaders, or potential leaders, of the next government commenced singing from the Sinn Féin hymn sheet, the DUP was spooked and the battles of the Home Rule episode in Northern politics were awakened.
The utterances of Randolph Churchill's aggressive and inflammatory language of 1886 when he declared "Ulster will fight and Ulster will be right" was a clear warning. Mr Randolph was a member of the Tory Party which was in opposition to the Liberals, kept in power only by the votes of the Irish Parliamentary Party, and the condition of that support was the passing of a Home Rule Act.