In 1912 the British government introduced a third home rule bill in Parliament. The bill polarized Irish society. Unionists in the northern province of Ulster soon founded a paramilitary army called the Ulster Volunteer Force (UVF) to shield the province from home rule. In response, nationalists organized the paramilitary Irish Volunteers to press for Irish self-government. The threat of civil war intensified.

The crisis was temporarily averted by the outbreak of World War I (1914-1918), and unionists and nationalists alike fought in the United Kingdom�s war effort against Germany. Indeed, members of the UVF and Irish Volunteers became core units of the British army on the war�s western front. However, one splinter group of Irish Volunteers�a forerunner of the Irish Republican Army (IRA)�refused to join the war effort. Instead, on Easter Monday in 1916, they organized the Easter Rebellion and declared the independence of Ireland. The rebellion, largely confined to Dublin, was suppressed, and the British government executed 15 Irish nationalist leaders and imprisoned many others.

The executions and imprisonments outraged the Irish population and set the stage for the emergence of Sinn Fein as the country�s dominant political party. Sinn Fein now firmly rejected home rule, which would have preserved the Irish-British union under the monarchy, and demanded the complete separation of Ireland from the United Kingdom. In the national election of 1918 Sinn Fein won 73 of 105 seats allotted to Ireland in the British Parliament. Sinn Fein�s dramatic electoral victory swept aside moderate home rule nationalists, who had held sway in Ireland prior to the outbreak of World War I.

In January 1919 Sinn Fein�s successful candidates, who had refused to take their seats in Parliament, met in Dublin and established their own revolutionary congress, the D�il �ireann (Gaelic for �Assembly of Ireland�). They proclaimed Ireland�s independence and formed a government with Sinn Fein leader Eamon de Valera as president. On the day the D�il first met, a group of Irish Volunteers launched an attack on the Royal Irish Constabulary (RIC), a British police force. (In August 1919 these insurgents would proclaim themselves the Irish Republican Army.) A campaign of guerrilla warfare against the British administration in Ireland ensued. The British soon brought in auxiliary English police recruits, known from their uniforms as the Black and Tans, who mounted ruthless reprisals.

The bitter violence served to unite much of Ireland against British rule. With a guerrilla war raging, the British government attempted to impose a settlement in December 1920 with the passage of the Government of Ireland Bill. The legislation divided Ireland into two self-governing areas. It provided one parliament for the six counties of the predominantly Protestant north (Northern Ireland) and another for the remaining 26 counties in the overwhelmingly Catholic south. The people of Northern Ireland accepted this limited home rule and elected a separate parliament in May 1921. Efforts to implement the new government in the other 26 counties, however, served only to solidify Sinn Fein�s demand for a fully independent Irish republic.

By 1921 hundreds of people had died in the ugly war of attacks and reprisals. Facing the prospect of a prolonged and bloody conflict, the British government issued a call for peace talks. The fighting ended with a truce in July 1921. Peace negotiations between representatives of the D�il and the British government of Prime Minister David Lloyd George produced the Anglo-Irish Treaty, signed in December. Under the treaty, the 26 southern counties would become the Irish Free State as a dominion within the British Commonwealth of Nations. Ireland would have a status equal to the other Commonwealth dominions of Canada, Australia, New Zealand, and South Africa. Like these other dominions, Ireland would be required to pledge an oath of allegiance to the British monarch. The United Kingdom would retain certain naval bases, but the Free State government would control its own police and armed forces. At the head of the new government there would be a governor-general representing the British king, but appointed on recommendation of the Free State government.

After heated debate the D�il ratified the treaty on January 15, 1922, by a vote of 64 to 57, thus ending what has come to be known as the Irish Revolution. Sinn Fein, however, split over the issue of ratification into pro- and anti-treaty factions, as did the IRA. Few saw the treaty as a victory. De Valera and his followers vigorously opposed the requirement of an oath of allegiance to the British crown. Pro-treaty forces, led by Arthur Griffith and Sinn Fein leader Michael Collins, regarded the agreement as merely an interim step toward full independence. They believed that further concessions from the British were not attainable and that rejection of the treaty would result in renewed fighting and probable defeat at the hands of the British. De Valera resigned as president of the D�il following the treaty�s ratification. Griffith replaced de Valera as president, and Collins became chairman of the provisional government.