Under the leadership of De Valera the dissident Sinn Féin
group, known as Republicans, called for a resumption of the struggle
against Britain. The majority of the IRA were also anti-Treaty,
and became known as the Irregulars.
After a six-month period in which positions were consolidated and
attempts at reconciliation were made, government troops attacked
the headquarters of the Irregulars in the Four Courts building in
Dublin in June 1922, initiating the Irish Civil War.
By August of that year the pro-Treatyites, better organised and
supported with British aid, had retaken control of all of the country's
urban area. There followed a protracted guerrilla campaign by the
Irregulars, recalling the tactics used in the Anglo-Irish War of
However, following the death of the vehement anti-Treaty leader
Liam Lynch in April 1923, a ceasefire was called, operative from
Meanwhile, the Provisional Government, headed by William Thomas
Cosgrave after the assassination of Collins in August 1922, drafted
a new constitution providing for a bicameral legislature, the Oireachtas,
comprising Dáil Éireann (Assembly of Ireland) and Seanad Éireann
(the Senate), nominally headed by the British monarch, represented
by the Governor-general.
The constitution was ratified by the Dáil in December 1922 and
the Provisional Government was dissolved. The official government
of the Irish Free State was instituted at once, with Cosgrave assuming
office as president of the Executive Council.