The guerrilla phase of the Irish Civil War began in August 1922, when the forces of the Irish Free State took all the fixed positions previously held by the Anti-Treaty IRA.

The IRA then waged a guerrilla war to try to bring down the new Irish Government and overturn the Anglo-Irish Treaty. This guerrilla campaign was ultimately defeated.

The IRA called a ceasefire in April 1923 and "dumped arms" the following month. This phase of the war was characterised by small-scale military actions but also by assassinations and executions on both sides. The Free State also imprisoned up to 13,000 IRA fighters. In addition, the campaign saw the destruction of a great deal of infrastructure such as roads and railways by the IRA.

Government victories in the major towns inaugurated a period of guerrilla warfare. After the fall of Cork, Liam Lynch ordered Anti-Treaty IRA units to disperse and form flying columns as they had when fighting the British.

They held out in areas such as the western part of counties Cork and Kerry in the south, County Wexford in the east and counties Sligo and Mayo in the west. Sporadic fighting also took place around Dundalk, where Frank Aiken and the Fourth Northern Division of the Irish Republican Army were based and Dublin, where small scale but regular attacks were mounted on Free State troops.

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