BELFAST, Northern Ireland—For more than a week earlier this month, Northern Ireland was rocked by riots in pro-British unionist communities, with frequent outbursts of violence in areas bordering on pro-Irish nationalist neighborhoods.

The Protocol has reaffirmed Unionism's worst fears that Northern Ireland is the unwanted child of the British government.

Republican sentiment is rising over fears that Brexit will tank the economy, but Northern Ireland’s unionists won’t go quietly.