The abolition of proportional representation in 1929 meant that the structure of party politics gave the Ulster Unionist Party a continual sizeable majority in the Parliament of Northern Ireland, leading to fifty years of one-party rule. While nationalist parties continued to retain the same number of seats that they had under proportional representation, the Northern Ireland Labour Party and various smaller leftist unionist groups were smothered, meaning that it proved impossible for any group to sustain a challenge to the Ulster Unionist Party from within the unionist section of the population.