In trying to make sense of the worst disturbances in Northern Ireland for years, there are two symmetrical pitfalls to be avoided. One is to present the recent violence as a simple reflex of Brexit, drawing a straight line between Boris Johnson’s campaign bus and a burning bus on the Shankill Road, while ignoring the local factors at work. The other is to overlook the many ways in which choices made at the highest levels of the British state have unsettled the region and added to the stock of combustible material.