I've just read a very good article by Andy Bielenberg of UCC (Cork) in the journal Past and Present, on the vexed question of the experience of the southern Ireland's Protestant minority during the Irish Revolution of 1916-23. It has been claimed that republican violence at times amounted to ethnic cleansing of Protestants. Commentators such as Eoghan Harris have claimed that up to 70,000 Protestants were forced out of the new state.
Bielenberg shows that, the Protestant population of the 26 counties fell from 1911-1926 by 106,000 and that this peaked in 1921 and 1922. But on the other hand, he calculates that no more than 16,000 and perhaps as few as 2,000 were forced to leave by violence (which intentionally or otherwise killed about 100 Protestant civilians). A total of the 20,000 'southern loyalists' sought refuge in Britain but many of these were Catholics.
The remainder is accounted for by the withdrawal of the British Army and civilian administration (30,000 plus unspecified number of secondary workers), First World War deaths (5,000 Protestants), voluntary migration, c.40-50,000, based on a 10% share of total emigration in those 15 years. Though some of the Protestant migration in the latter was caused by dislike of Irish independence and accelerated land reform taking away the remaining estates of the gentry and associated jobs.
In short Protestants were vulnerable in this period, especially in rural areas, but not subject to systematic campaigns of ethnic cleansing or murder.