Birth of Northern Ireland
The origin of the religious discrimination in Northern Ireland dates back to the reign of Scottish born-English King James 1st of England who planted 6 counties of Ulster with English and Scottish settlers and drove the Irish from their homes. While the Irish were Catholic, the majority of the settlers, where were Scottish were Presbyterians.
Presbyterians are members of a Protestant church which is governed by elders who are all of equal rank rather than bishops. How did the Irish feel about this after they were driven off their land and into the bog and the mountains? There were angry and upset but they were determined to keep their native Irish under control. Thus started numerous political and religious conflicts which continued for centuries only for the fighting to end thanks to the many political talks that vowed to end discrimination against Catholics and Protestants. Political conflicts as Protestants in the planted counties (mainly the ones that make up the six counties of Northern Ireland) are Unionists who want to be part of the United Kingdom. They would lose control if Ireland were united into a single country to a Catholic and Nationalist majority.
As a result, Northern Ireland was created on 23 Dec 1920 with the passing of the Government of Ireland Act (while it would commence on 3 May 1921), it gave the Protestant Unionists a piece of Ireland were the majority of Nationalist and Catholics is small as well as giving the remaining 26 counties of Ireland independence from British rule (well, free from Westminster).