The post-war years were relatively placid in Belfast, but sectarian tensions and resentment among the Catholic population at widespread discrimination festered below the surface, and the city erupted into violence in August 1969 when sectarian rioting broke out in the city. The perceived one-sidedness of the police and the failure of the IRA to defend Catholic neighbourhoods of the city was one of the main causes of the formation of the militant Provisional Irish Republican Army (PIRA), which would subsequently launch an armed campaign against the state of Northern Ireland.