1905
Sinn Féin ("We Ourselves") founded in 1902 by Arthur Griffith, became a political party; initially it was largely a pacifist, propagandist organisation promoting Irish economic welfare and full independence. 

1914
Implementation of the Third Home Rule Bill, introduced in 1912 and passed by the House of Commons in 1913, suspended on the outbreak of World War I. Pro-British nationalists established paramilitary Ulster Volunteer Force to resist Home Rule. The Irish Volunteers, subsequently formed by nationalists as a rival military force, was the core of what by 1919 had become the Irish Republican Army (IRA).

1916
Easter Rising, armed uprising in Dublin, suppressed after six days by British troops. The executions that followed gained many new recruits for the Irish cause.

1917
Sinn Féin adopted a revolutionary and republican constitution. Subsequently, under Eamon de Valera, one of the leaders of the Easter Rising, it became the dominant party in Ireland, excluding Ulster.

1919
After winning almost all the Irish seats outside Ulster in the 1918 general election, Sinn Féin established an Irish parliament, the Dáil Éireann, in Dublin, and set up its own administration. 

1919-1921
War of Independence, precipitated by the killing of two members of the armed police force by Volunteers. The British authorities introduced the "Black and Tans" in response to the IRA's successful use of guerilla tactics.

1920
Government of Ireland Act effectively partitions Ireland by establishing separate home-rule parliaments- one for the six Protestant-dominated counties of Ulster and one for the rest of the country.

1921
The Ulster parliament established in June. The Anglo-Irish Treaty, providing for a self-governing Irish Free State with dominion status, was signed on December 6, passed by Dáil Éireann on January 7, 1922, and came into effect on December 6, of that year.

1922-1923
The Irish Civil War, caused by a split within Sinn Féin and the IRA over the signing of the Anglo-Irish Treaty: Michael Collins was a leader of the pro-Treaty faction; De Valera of the anti-Treaty group. The pro-Treaty group was ultimately victorious and went on to form the governments of the Free State as the Cumann na nGaedheal Party, later Fine Gael.

1926
Sinn Féin split again over recognition of the legitimacy of the Free State. De Valera led the pro-recognition majority out of the party and established the Fianna Fáil Party.

1931
The Statute of Westminster enacted, recognising the legislative autonomy of the British dominions and establishing the Commonwealth.

1932
Fianna Fáil was elected to government, and remained in power until 1948. De Valera began implementing more radical policies, including the repeal of a law restricting IRA activities, abrogating the oath of allegiance, and withholding certain land annuity payments to Britain, which led to a six-year tariff war.

1937
The new republican constitution was approved in a referendum. The Irish Free State was replaced by Éire, and remaining constitutional ties with Britain were severed.

1938
Irish writer and patriot Douglas Hyde became the first president of Éire, and De Valera its first prime minister. The tariff war with Britain was ended.

1939
Éire declares itself neutral on the outbreak of World War II.