LONDON — The Democratic Unionist Party, the hard-line Northern Irish Protestant party that essentially has both Prime Minister Theresa May and the Brexit process in a death grip, is not merely stupid or fanatical. The party understands that its fortunes depend on an increasingly threatened British nationalism.

Unionism is dying in Northern Ireland. During the 30-year war, the Protestant majority was mostly loyal, even though Northern Ireland was one of the the poorest parts of the United Kingdom. With a dwindling industrial base, it was subsidized by war, infused with money for an occupying army and giant, garrisoned stations full of police officers.

When I was growing up in the 1980s, in a small Protestant town in the east of the six counties, Protestants could believe that those men of violence were there for us, that the Union was ours. Electoral gerrymandering shored up Unionist power. There were jobs for the “Prods,” as Protestants were known. Protestants occupied most of the skilled work and the few professional and managerial jobs available. The south of Ireland was poor, and everyday chauvinism said Catholics were poor because they were backward and dirty, and brought it on themselves. “That’s a Protestant-looking house,” mothers would chirp after tidying up.

The annual Twelfth of July bonfires and parades, celebrating the history of Ulster Loyalism, saw effigies of wicked Papists burned for public edification and the delight of inebriated Loyalists. This was “our culture.” These festivities helped create a lynch mob atmosphere, leading to the murder of Catholics. Every year, the stories were the same: Bonfire night was a night for petty terror and bricking Catholic windows. Parades day was a day for blood. I recall that one year during my childhood, members of a local Loyalist flute band stabbed a Catholic bus driver repeatedly; a woman tried to stanch the bleeding by wrapping him in towels, but when the ambulance arrived, he was dead. We heard this story on the radio, on the way back from watching a parade. Many paid with blood for Protestant loyalty to Britain.