The Four Courts had been occupied by Anti-Treaty militants, since 14 April 1922. The Pro-Treaty side saw this as an act of rebellion but Michael Collins had wanted to avoid a Civil War at all costs.
By June 1922, the British cabinet actually resolved to attack the Four Courts themselves but instead gave Collins one last chance to clear the Four Courts himself.
Following a final ultimatum given on 27 June, Collins decided to bombard the Four Courts garrison into surrender. The government then appointed Collins as Commander-in-Chief of the National Army.
After three days of bombardment (28–30 June 1922), the anti-treaty garrison in the Four Courts surrendered following the storming of the building and a massive explosion which left priceless manuscripts floating over the city for several hours afterwards.