London basically lost interest in NI after devolution and left it to the local unionists, the major party, to run the show. Local nationalists largely opted out because they wanted a United Ireland. Until Direct Rule was introduced in 1972, and a few years before that, NI really only featured in London plans during WWII.
During the first 50 years of NI's existence the vast bulk of the power, privilege and discrimination lay with unionists and in the past 30 years nationalists have achieved a position where they now have more say than unionists, especially since the the Anglo-Irish Agreement in 1985.
The three major religious denominations in NI are roughly, Catholic 40%, Presbyterian 20% and Church of Ireland 15%. CoI have gone from being top dog so far as power was concerned in the late 1800s for the whole island to third place - or less - in NI now.