Irish independence in 1921 resulted in partition. The six northeastern, largely Protestant counties became Northern Ireland, part of the United Kingdom. The territory's 1.5 million inhabitants may be divided into Unionists (largely Protestants), those who seek to maintain the union with the United Kingdom, and Nationalists (largely Roman Catholics), those who desire unification with Ireland. The terms Loyalist and Republican are frequently used to refer to (respectively) Unionists and Nationalists who would contemplate the use of force to achieve these goals.

Northern Ireland maintained its own government from 1921 to 1972. During this period the Unionist Party had exclusive power, and deep distrust existed between both communities. The system of a government with a single-party majority with no tradition of judicial protection for human rights could not accommodate this division. Religious and political discrimination against Catholics soon became widespread.

This "factory of grievances" provoked civil rights protests in the 1960s...