Why is part of Ireland owned by the UK?

Related questions

1. Is Northern Ireland poorer than Ireland?
2. What is Ireland's main export?
3. Is Ireland a third world country?
4. What was the IRA fighting for?
5. Has Ireland paid back the bailout money?
6. What are 3 interesting facts about Ireland?
7. Are the Irish a race?
8. Why did Bloody Sunday happen?
9. Is Dublin Ireland expensive?
10. What is the most peaceful country in the world?

Tags

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2. #great
3. #wanted
4. #northern
5. #state
6. #become
7. #protestant
8. #population
9. #irish
10. #unionists
11. #which
12. #southern
13. #ireland
14. #united
15. #within
16. #remain
17. #britain
18. #would
19. #unlike
20. #kingdom
21. #colonists
22. #these
23. #descendants