The vast majority of Irish Protestants are actually Scotch-Irish (aka Ulster Scots), that is the descendants of Scottish people who were encouraged by British authorities to colonize Ireland beginning in the 17th century. The Ulster Scots were allowed to settle on land that had been confiscated from Gaelic/Native Irish people (who were and are Catholic). The British did this to punish the rebellious Gaels and replace them with a relatively loyal demographic. The Catholic/Gaelic people of Ireland obviously resented the Ulster Scots for collaborating with the British and taking their land, and they have been fighting each other on and off ever since.

This alliance between Protestant Ulster Scots and the British government remains today, as does the enmity between Catholic/Gaelic people and Protestant/Ulster Scots people.