The Brexit referendum of 2016 triggered one of the most profound constitutional crises in modern British history. A wave of populist nationalism gave way to political and economic instability, throwing the future of the United Kingdom into sharp relief. The Scottish National Party saw an opportunity to press for a second referendum on Scottish independence with Irish republicans lobbying the British Government for a border poll in a move to help secure their goal of a United Ireland. For Unionists in Northern Ireland, a referendum that began on the question of sovereignty quickly degenerated into cries of betrayal and a redrawn border in the Irish Sea. Extraordinary uncertainty now hangs over the future of the Union between Great Britain and Northern Ireland. In Northern Ireland's centenary year, military and political historian Aaron Edwards, a native of Belfast, explores the profound challenges facing Unionists. He reflects upon the past century of political turbulence on these islands, the effects of Republican violence on the Unionist psyche and the embattlement of a people who believe themselves to be once again under siege.