Well, if you really want to get down to root causes, if Richard, Duke of York, had not been named Governor of Ireland in 1449 then you would not have had the amnity between the Celts and the Saxons which manifested itself in 1860. </sarcasm>
As usual, you have your history wrong. From: (Richard of York).
In 1449 Richard, Duke of York, was appointed governor of Ireland and made a great impression on the Irish and Anglo-Irish. When Richard of York challenged for the throne Ireland supported him.
Richard's perhaps illegitimate son, Edward IV, King of England, had trouble with the Irish. And of course, Richard was a Plantagenet, not a Saxon (though I haven't traced his family line).