I don't think it was me recently but I might have in the past.
Ireland has a history of English colonisation from the 12th century down but a big event was when the stuarts kicked a lot of the Irish out of their land and gave it to settlers or "planters" mostly from Scotland and especially in the North.
This is the origin of the Ulster Protestants.
There were in Victorian times a lot of movements for Irish home rule and various times of unrest. (skip all the complex stuff here)
When Lloyd George came finally to grant home rule in 1921 he found himself in a position where he couldn't simply say to the Ulster Unionists sorry guys the majority have spoken because he needed their support to stay in power so partition happened.
This caused major ructions in the new republic (it was the "free state" then) and a civil war between those who had supported the treaty and those who were holding out for all Ireland.
That civil war killed more than died in the Troubles!
Had Lloyd George had a stronger majority Ireland might have been independant as a whole and the fighting might have been with Dublin and not with London