I have recommended this book elsewhere on the subreddit, but from a 20th century angle I really rate Making Sense of the Troubles by David McVea and David McKittrick. It explains, in a clear and non-partisan way, the context and effects of the 1922 partition of Ireland, which was the root cause of violence in the North. Of course, you might want to hold off on reading this until you've covered more of the earlier historical material.

I'm Northern Irish but living in England myself, so - as an aside - I'm glad to see you taking an interest.

But how "English" were the Normans, given that they had only conquered England itself a century earlier? And to what extent should they be seen as invaders, and to what extent the invited guests of Irish actors, attempting to leverage external power to settle internal conflicts?

I've answered this question in part elsewhere, but you would be surprised how quickly the Normans in England Anglicised themselves. Partly this was a linguistic factor - the new Anglo-Norman elite speak a variety of French dialects from Norman, Breton and Piccardy to even Occitan, and combine this with Old English to create a language that within a generation is markedly distinct from the French spoken even in Normandy - and largely a result of widespread integration into the pre-existing English and British social hierarchy. This is a very prevalent and largely successful Norman tactic designed to expiate as much as possible the social upheaval caused by conquest.

The results of this manifest themselves most noticably in the new cohort of Anglo-Norman writers who largely appear in the twelfth century. Prominent writers such as William of Malmesbury, Orderic Vitalis, Gerald of Wales and likely Geoffrey of Monmouth, are all of mixed Norman and English or Welsh heritage, a fact that many such as Gerald and Orderic address in their writings, and perceive of themselves very much as English, or in Gerald and Geoffrey's case, Welsh. Higher up the social strata, William I's son Henry I marries Matilda, the daughter of Malcolm III and Margaret of Scotland, who was the grandaughter of Edmund Ironside, further legitimising the Norman dynasty by re-integrating it with the Anglo-Saxon Cerdicing royal house of Wessex.

Gerald of Wales, or de Barri, provides us with some of our most interesting sources on the conquest of Ireland. Gerald is the nephew of leading figures in the conquest Robert Fitz-Stephen and Raymond FitzGerald, and writes two books on Ireland, the Topographia Hibernica - a general history and guide to Ireland - and the Expugnatio Hibernica - an account of the conquest itself, on which he accompanies his uncles. What quickly becomes clear in Gerald's writing is his sheer loathing of the Irish. He despises them. They are a filthy, barbarous people living in sin and almost entirely without any virtues. Gerald even takes time in his other writings on the history of Wales in his Descriptio Cambriae to say that although the Welsh used to be a sinful people, particularly in regard to sodomy, they are now much reformed and have come so far, but at any rate were never as bad as the Irish, who are probably beyond saving.

The Topographia contains increasingly outlandish portrayals of bizarre Irish superstitions, rites, practices and customs, including a coronation ceremony involving bestiality and bathing in soup. This, of course, is all a colossal act in self-justification. In Gerald's constructed world, the Irish are poor, ignorant savages who clearly cannot be trusted to look after themselves, and desperately need the English (although most of those leading the conquest were actually Cambro-Norman) to come in, take over both politically and religiously, and put them on the right track.

In Gerald's Expugnatio, Diarmait Mac Murchada is deposed as high king and flees to Bristol (which would have had extensive trade links with Ireland, particularly the Hiberno-Norse settlements in Wexford and Waterford), where he begs for English assistance, and the Marcher Lords including Gerald's uncles respond purely out of the goodness of their hearts. Diarmait is so grateful, according to a speech supposedly given by Robert Fitz-Stephen on the eve of battle, that he has decided to reward all of the English with land. One can only imagine what Diarmait would have made of such a speech, although of course he would have been powerless to deny it. This is further justification by Gerald of what is essentially an opportunistic land-grab by the Anglo-Welsh marcher lords, exploiting political upheaval for their own gain and couching it in terms of political intervention and cultural and spiritual salvation.

While I cannot give you a very detailed response at this time, I can offer some suggestions for reading on medieval Ireland. Katharine Simms "From Kings to Warlords," while perhaps slightly dated at this point, still addresses some key aspects of medieval Irish society and the extent to which a "Gaelic revival" occurred in the later middle ages after the Anglo-Norman invasion.

Similarly, Robin Frame's "Colonial Ireland" is an excellent survey of the emergent Anglo-Norman colonies in Ireland after 1169.

Daibhi O'Croinin's Early Christian Ireland 400-1200 touches on some aspects of the early Anglo-Norman invasion, but naturally cuts off quite soon into that era.

Gaels and Gaelicized Ireland in the Middle Ages by Kenneth Nicholls is likewise dated (even moreso than Simms) but still a decent resource.

These were just off the top of my head, I am at work now and cant access all the books and resources I have stockpiled at home. I would also encourage you to take advantage of the CELT project run by University College Cork: its an online database including a pretty large list of primary sources with English translations. Oftimes the translations are quite old, but reading the various annalistic sources for yourself, as well as some of the prose and poetic works, can provide some valuable insight into the period. Though, they are best read when accompanied by a grounding in some of the secondary research so that one understands the contexts, biases, and histories associated with each primary document.

Hope that helps, and hopefully another user comes along to provide a more detailed response!