Why is there a crisis in Northern Ireland at the moment ?
First, because of Brexit. If you create a border where none existed, you cause problems for trade. When Northern Ireland has been seamlessly intergrated in to the economies of the Republic and Britain, problems are bound to be created,
Second, because neither of the parties (DUP and Conservatives) who were so enthusiastic for Brexit were never willing to face up to the consequences of their enthusiasm.
Third, if tensions start to escalate, nobody has 'taken back control'. On the contrary, the situation begins to take control of the participants.
Of course, there are other reasons. But Brexit, and its unfolding disaster, is the most important proximate cause. It is necessary to remind ourselves just how irrational and ideological this project is.