Beginning with the removal of British troops and administrators in the spring of 1922, this chapter highlights the fact that the Irish Civil War (1922–1923) was only one of a number of internecine civil conflicts in Ireland that took place both within and between the two new partition states. As with many other postcolonial states, both new Irelands had a very similar experience and response to devolved power, facing as they did severe political and military opposition from their new religious and political minority populations. Both would use harsh and unprecedented state coercion to quell this opposition through the use of internment, torture and summary execution. The main focus, however, concerns the undeclared civil war between north and south in the first six months of 1922, when, under the leadership of Michael Collins, the new provisional government launched a sustained political, diplomatic, economic and military campaign against the new Belfast government. This chapter explores the deep ambiguities that underlay this campaign, the reasons for its failure to significantly alter the partition settlement and its traumatic effects on the character of the unionist government and the Ulster population as a whole.