The period from 1970 through 1972 saw an explosion of political violence in Northern Ireland, peaking in 1972, when nearly 500 people, just over half of them civilians, lost their lives. The year 1972 saw the greatest loss of life throughout the entire conflict.[64]

In Derry by the end of 1971, 29 barricades were in place to block access to what was known as Free Derry; 16 of them impassable even to the British Army's one-ton armoured vehicles.[65] Many of the nationalist/republican "no-go areas" were controlled by one of the two factions of the Irish Republican Army—the Provisional IRA and Official IRA.

There are several reasons why violence escalated in these years.

Unionists claim the main reason was the formation of the Provisional Irish Republican Army (Provisional IRA), a group formed when the IRA split into the Provisional and Official factions. While the older IRA had embraced non-violent civil agitation,[66] the new Provisional IRA was determined to wage "armed struggle" against British rule in Northern Ireland. The new IRA was willing to take on the role of "defenders of the Catholic community",[67] rather than seeking working-class unity across both communities which had become the aim of the "Officials".

Nationalists pointed to a number of events in these years to explain the upsurge in violence. One such incident was the Falls Curfew in July 1970, when 3,000 troops imposed a curfew on the nationalist Lower Falls area of Belfast, firing more than 1,500 rounds of ammunition in gun battles with the IRA and killing four people. Another was the 1971 introduction of internment without trial (out of over 350 initial detainees, none was a Protestant).[68] Moreover, due to poor intelligence,[69] very few of those interned were actually republican activists, but some went on to become republicans as a result of their experience.[citation needed] Between 1971 and 1975, 1,981 people were detained; 1,874 were Catholic/republican, while 107 were Protestant/loyalist.[70] There were widespread allegations of abuse and even torture of detainees,[71][72] and the "five techniques" used by the police and army for interrogation were ruled to be illegal following a British government inquiry.[73] Nationalists also point to the fatal shootings of 14 unarmed nationalist civil rights demonstrators by the British Army in Derry on 30 January 1972, on what became known as Bloody Sunday. The Provisional IRA (or "Provos", as they became known), which emerged out of a split in the Irish Republican Army in December 1969, soon established itself as defenders of the nationalist community.[74][75] Despite the increasingly reformist and Marxist politics of the Official IRA, it began its own armed campaign in reaction to the ongoing violence. The Provisional IRA's offensive campaign began in early 1971 when the Army Council sanctioned attacks on the British Army.[76]

In 1972, the Provisional IRA killed approximately 100 soldiers, wounded 500 more and carried out approximately 1,300 bombings,[77] mostly against commercial targets which they considered "the artificial economy".[78][79] The bombing campaign killed many civilians, notably on Bloody Friday on 21 July, when 22 bombs were set off in the centre of Belfast killing seven civilians and two soldiers. The Official IRA, which had never been fully committed to armed action, called off its campaign in May 1972.[80] Despite a temporary ceasefire in 1972 and talks with British officials, the Provisionals were determined to continue their campaign until the achievement of a united Ireland.