The Great War was the single most crucial factor influencing the course of Irish history from the second decade of the 20th century, creating circumstances which led to total and irreversible political polarisation and to partition in Ireland. Initially it split the Irish Volunteers, who were raised to safeguard the granting of Home Rule and resist the secession of Ulster by the Ulster Volunteers from what they claimed was a coercive All-Ireland Home Rule settlement, into two opposing camps. These were, the larger National Volunteers – supporting the Allied war effort and subsequently in combat on the Western Front and in Gallipoli. And secondly the minority group of Volunteers who remained in Ireland and staged the Easter Rebellion in April 1916, proclaiming an Irish Republic, virtually unimaginable without the backdrop of the European conflict.