The guerrilla war that redrew the map of Ireland
Between 1919 and 1921, a localized conflict escalated into a brutal struggle for sovereignty. What began as targeted ambushes by the IRA transformed into a widespread campaign of reprisals, sectarian violence, and civil disobedience that ultimately fractured the island into two distinct political entities.
The conflict, often called the Anglo-Irish War, emerged from the momentum of the 1916 Easter Rising. While that initial insurrection was suppressed within a week, the British execution of its leaders galvanized Irish nationalist sentiment. By the 1918 general election, the republican Sinn Féin party achieved a landslide victory, winning 73 of 105 Irish seats and establishing a breakaway government known as Dáil Éireann. This new administration declared independence on 21 January 1919, the same day IRA volunteers launched the Soloheadbeg ambush.
The war was characterized by asymmetric tactics. The IRA utilized 'flying columns'—small, mobile units of 20 to 100 men—to ambush patrols and attack barracks. In response, the British government deployed paramilitary forces like the 'Black and Tans' and the Auxiliaries. These reinforcements became notorious for retaliatory attacks on civilians, leading some to label the period the 'Black and Tan War.' The violence reached a peak in late 1920; notably, during 'Bloody Sunday' in Dublin, the RIC opened fire on a crowd at a Gaelic football match in Croke Park, resulting in 14 civilian deaths and 6'5' injuries.
The struggle also held a deep sectarian dimension, particularly in the northeast. In Ulster, a Protestant majority formed the Ulster Special Constabulary to resist Home Rule, leading to intense conflict in Belfast that killed nearly 500 people, mostly Catholics. The war concluded with the 1921 Anglo-Irish Treaty, which established the Irish Free State as a self-governing dominion while leaving Northern Ireland within the United Kingdom. However, the treaty's terms sparked an eleven-month civil war among Irish republicans, leaving a legacy of division that persisted long after the 1921 ceasefire.
Source: Irish War of Independence
