The Irish Civil War was a conflict that accompanied the establishment of the Irish Free State

Irish Free State

The Irish Free State was the state established as a Dominion on 6 December 1922 under the Anglo-Irish Treaty, signed by the British government and Irish representatives exactly twelve months beforehand...

 as an entity independent

Independence

Independence is a condition of a nation, country, or state in which its residents and population, or some portion thereof, exercise self-government, and usually sovereignty, over its territory....

 from the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 within the British Empire

British Empire

The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom. It originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height, it was the...

.

The conflict was waged between two opposing groups of Irish nationalists

Irish nationalism

Irish nationalism manifests itself in political and social movements and in sentiment inspired by a love for Irish culture, language and history, and as a sense of pride in Ireland and in the Irish people...

: the forces of the "Provisional Government"

Provisional Government of Southern Ireland

The provisional Government of Southern Ireland was the provisional government for the administration of Southern Ireland between 16 January 1922 and 6 December 1922. The government was effectively a transitional administration for the period between the ratifying of the Anglo-Irish Treaty and the...

 that established the Free State in December 1922, who supported the Anglo-Irish Treaty

Anglo-Irish Treaty

The Anglo-Irish Treaty , officially called the Articles of Agreement for a Treaty Between Great Britain and Ireland, was a treaty between the Government of the United Kingdom of Great Britain and Ireland and representatives of the secessionist Irish Republic that concluded the Irish War of...

, and the Republican

Irish Republicanism

Irish republicanism is an ideology based on the belief that all of Ireland should be an independent republic.In 1801, under the Act of Union, the Kingdom of Great Britain and the Kingdom of Ireland merged to form the United Kingdom of Great Britain and Ireland...

 opposition, for whom the Treaty represented a betrayal of the Irish Republic

Irish Republic

The Irish Republic was a revolutionary state that declared its independence from Great Britain in January 1919. It established a legislature , a government , a court system and a police force...

. The war was won by the Free State forces.

The Civil War may have claimed more lives than the War of Independence

Irish War of Independence

The Irish War of Independence , Anglo-Irish War, Black and Tan War, or Tan War was a guerrilla war mounted by the Irish Republican Army against the British government and its forces in Ireland. It began in January 1919, following the Irish Republic's declaration of independence. Both sides agreed...

 against Britain that preceded it, and left Irish society divided and embittered.