Ireland is Britain's closest neighbor—the sea crossing from Scotland measures only twelve miles. Ireland was also its first conquered territory in what became Britain's empire. The two nation's stories have been intertwined since Anglo-Norman invaders crossed the Irish Sea during the twelfth century. These Troubled Isles tells the extraordinary history of the past century in this tumultuous relationship, from the Anglo-Irish treaty of 1922 to the present day. This is a tale of deep division between Catholic nationalism and Protestant unionism, of wars and terrorist violence, and of occasional moments of great courage on the part of British and Irish leaders. Today, the post-Brexit weakening of the United Kingdom's constitutional ties has coincided with the march of demography in Northern Ireland as the Protestant unionist majority continues to shrink. Sinn Féin's historic string of electoral victories in Northern Ireland since 2022 has once more resurfaced the unfinished business of partition. Here, Philip Stephens explores how Ireland might escape its troubled past by deploying history to inform the future rather than hold it in place.