Answer:
the issue that caused tension in Northern Ireland is the conflict between Unionists/loyalists and Nationalists/republicans
Explanation:
In the Northern of Ireland is develop a conflict between to political parties in one side are the Union/loyalists these are mainly protestants and want Ireland to remain in the United Kingdom.
On the other side are the Nationalist/republicans who are mostly catholic and want Ireland to leave the United Kingdom and create a United Ireland.
