I’ve heard that eventually, Northern Ireland could be merged into the Republic of Ireland.
I’m not familiar enough with the history of why Northern Ireland was part of the UK. But, I thought the religious issue was a key issue, as the Republic of Ireland is largely Catholic, while Northern Ireland was mostly Protestant.
All of Ireland used to be part of the UK (United Kingdom of Great Britain and Ireland). In the 1920s most of Ireland gained it’s independence but Unionists (mostly Protestant) wanted to remain part of the UK. They were a minority in most of Ireland but a majority in the northeastern part of Ireland so 6 of the 32 counties remained part of the UK (United Kingdom of Great Britain and Northern Ireland). https://en.wikipedia.org/wiki/Partition_of_Ireland
The outcome is Very ironic .
London is booming so why live in cold rainy sunless Belfast .