In December 1921, Sinn Fein negotiators signed a compromise treaty with the British government which created the Irish Free State, a self-governing dominion, for the twenty-six counties of southern Ireland. Its terms generated turmoil. Within months, Ireland erupted into a devastating civil war that ripped not only Sinn Fein, the IRA and its female wing Cumann na mBan asunder, but also local communities and families. Although its death toll suggests a conflict less severe than other European civil wars, it has a harrowing impact on the small island, including public rows and recriminations and deep, often private traumas. The long shadow it cast, socially, economically and politically, endured. 

It was only in 2020 that Fine Gael and Fianna Fail, the two parties which grew out of the rival factions, could see their way to officially sharing power. Drawing on many previously unpublished sources and newly released archival material, one of Ireland's most renowned historians lays bare the course and impact of the war, the lives it cost, the reputations it forged, the fate of its survivors and how this tragedy shaped modern Ireland.