When did the Troubles begin? Was it when the first stone was thrown or the first shot fired? Or did they begin earlier with a police baton blow? Or earlier still with a peaceful march demanding civil rights? As with almost anything to do with Northern Ireland’s turbulent political past, the moment is contested. For me, they began on 30 November 1968, when, as a young lad, I attended a civil rights march in my home town, Armagh.

The Northern Ireland Civil Rights Association (Nicra) had been formed the year before by a broad coalition – trade unionists, radical socialists, republicans and members of the Northern Irish Labour and Liberal parties – with the same basic aim: to challenge anti-Catholic discrimination in jobs and housing. One of its defining slogans was the now quaintly sexist “One man, one vote”, which demanded an end to the system of plural voting that prevailed in Northern Ireland long after it had been abolished in the rest of the UK. To be eligible to vote in a local election in Northern Ireland you had to be a homeowner, most of whom were middle- and upper-class Protestants. Many of them were business owners, which entitled them to several extra votes.

To make matters worse, the state also employed gerrymandering (manipulating ward boundaries in local elections to maintain a false unionist majority). This meant that in 1968 in predominantly Catholic Derry, where the total nationalist vote was 14,000 and the unionist vote 9,000, the local council comprised 12 unionist and eight nationalist members. Since its inception in 1921, when Ireland was partitioned, Northern Ireland, though remaining part of the UK, was a place apart. One of its founders, Lord Craigavon, had promised “a Protestant parliament for a Protestant people”. Four decades later, the state was essentially and unapologetically biased in favour of its majority population in terms of the allocation of council houses and jobs.

When we saw police laying into marchers, it was as if something hidden and hateful had been pushed into the open Rory McShane, civil rights activist

For the majority of working-class Catholics who took to the streets in support of civil rights, the cause was personal as well as political. After they married, my parents were on a council house waiting list for 13 years, living for most of that time with my maternal grandparents. For that period and longer, neither of them had a vote in a local election. As with many of their generation, the civil rights protests signalled to them an end to the soul-sapping collective acquiescence that had prevailed in the province for so long, and led to an embrace of a late-flowering activism that was profoundly empowering.

I remember the day of the Armagh march well: the almost carnival atmosphere as the marchers, several thousand strong, set off from the Killylea Road, close to the housing estate I lived on. My parents joined the march, taking my younger brother and sister with them. My grandparents attended, as did most of my relatives and several of my school teachers and fellow pupils from the Christian Brothers’ grammar school. Almost everyone from Catholic housing estates in the town seemed to be there, as well as many prominent middle-class local figures. Protesters came from all over the north, and even from the south. Under the civil rights banner, trade unionists, Labour party members, radical socialists, communists and even anarchists united for a common cause, with ordinary, politically unaffiliated people believing, perhaps for the first time in their lives, that real change was a possibility.

All this came back to me a few months ago when I was asked by the Gallery of Photography Ireland to put forward an idea for an exhibition. The more I thought about it, the more it seemed crucial to evoke the sense of excitement and empowerment of that lost moment in 1968, before the Troubles reinstated an older narrative of violent Irish republicanism against British colonialism.

For many people, particularly in England, the Troubles are understood essentially as a war between the IRA, whose aim was to reunite Ireland, and the British security forces. The short-lived civil rights era of the late 60s and early 70s has been conveniently overlooked, perhaps because it illuminates the fact that the endemic discrimination in Northern Ireland was ignored for decades by successive Westminster governments of every political hue. In retrospect, though, it represents one of the great “what if?” moments when the violence that followed might have been averted through reform.

I have called the exhibition The Lost Moment (having decided after much deliberation not to place a question mark after the title) and it will open on 28 April in the Nerve Centre in Derry, a gallery housed in the former Ebrington army barracks that looked over the city throughout the Troubles. The show will include work by local and international photographers as well as films, projections and ephemera from the time in the form of political posters, periodicals and pamphlets. It is an attempt to evoke not just the spirit of idealism and protest, but also the anxieties and anger of the unionist counter-demonstrations that sprang up in reaction to it.

One of the aims of the exhibition is to place the Northern Irish civil rights movement in the context of other protest movements of the time. It was a struggle that adopted the nonviolent tactics espoused by Martin Luther King and his followers in America – even borrowing their gospel anthem, We Shall Overcome. Like that movement, it was a broad church – an approach with which its more radical supporters, particularly the young leftwing students who formed the more militant People’s Democracy party in 1968, quickly grew impatient. They looked instead towards the more confrontational actions on the streets of Paris and Chicago during the various revolutionary uprisings of that tumultuous year. Veteran Derry-based leftwing activist and political commentator Eamonn McCann, for instance, had attended the anti-Vietnam war protest in London’s Grosvenor Square in March of that year, which ended in a riot.

The first civil rights march, on 24 August 1968 in Dungannon. Photograph: Belfast Telegraph

Historian Paul Bew, one of several Protestant leftwing student activists at the time (and later an adviser to the former unionist leader David Trimble) says: “I don’t recall ever having a discussion about the border or the national question with any of the student protest leaders. It was all about Vietnam, Prague, Paris – those issues cut across the partisan politics of Northern Ireland and fed into the protests there.” One of the student leaders, Michael Farrell, later recalled how a group of activists went straight from an anti-Vietnam war protest outside Belfast city hall to the first civil rights march in Dungannon in August 1968, replacing the slogans on their placards along the way.

The march from Coalisland to Dungannon on Saturday 24 August 1968 drew 4,000 people, and despite a government ban and a vociferous loyalist counter-demonstration organised by the Rev Ian Paisley, passed off peacefully. McCann and his fellow activists immediately contacted Nicra with a request to hold another march in Derry on Saturday 5 October. At the 11th hour, it was banned by William Craig, the minister for home affairs, after a local loyalist organisation announced that they would hold a march along the same route on the same day.

The Derry activists decided to go ahead with the protest anyway, hoping their defiance would help attract an even bigger crowd. The ban had the opposite effect and only about 400 assembled at the start point, with another 200 curious onlookers lining the pavements. “It was a very disappointing crowd,” McCann later concluded. What subsequently happened, though, had a seismic impact way beyond Derry and Northern Ireland.

A poster announcing the Derry march that ended in disaster. Photograph: Nicra / Museum of Free Derry

The march ended almost before it began, when large numbers of Royal Ulster Constabulary (RUC) employed a tactic that decades later would be known as “kettling” – hemming in the protesters on Duke Street. Stewards urged the crowd to keep calm, but placards were thrown in frustration. Then all hell broke lose. Gaye O’Brien, a news cameraman from the Irish broadcaster RTE, was on hand to record the RUC’s response. The footage remains viscerally shocking to this day – baton-wielding officers wading into the crowd, felling young and old alike, cracking skulls as women scream and children scatter. An unsuspecting elderly man is struck from behind across the side of the face. Moments later, a breathless officer batons a marcher to the ground, his face twisted in fury, before he catches sight of the camera that has just captured his violence for posterity.

Among those who escaped serious injury that day, but underwent a dramatic political epiphany, was a young woman who would soon become one of the key figures in the years of ferment that were to follow. “You could feel the hatred,” Bernadette Devlin said decades later. “That’s my recollection of that day. It was my first realisation that the police hated us.”

Across the nationalist areas of the north, the scenes of police violence provoked a collective howl of anger. “People were outraged,” remembers Rory McShane, who in 1968 was president of the students’ union at Queen’s University in Belfast and a prominent civil rights activist. “When we saw the police laying into the marchers on the news, it was as if something hidden and hateful had suddenly been pushed out into the open.”

Coverage of the violence achieved more in terms of highlighting the plight of Northern Ireland’s Catholic minority than decades of dogged, but unproductive, campaigning by nationalist politicians. Derry suddenly became synonymous with Selma and the US black civil rights struggle led by the recently murdered Martin Luther King. If, as Devlin later put it, “television brought the world to our doorstep”, it also brought the civil rights cause in Northern Ireland to a global audience. “The Bogside was deluged with journalists,” recalled McCann. “A journalist from the Daily Mail came to my front door asking for the name and address of an articulate, Catholic, unemployed slum-dweller she could talk to. Derry was big news.”

The Belfast Telegraph, from November 1968, reports on the violence spiralling out from the Derry march. Photograph: The Belfast Telegraph

The immediate effect was about 2,000 students organised a march from the university to the city hall in protest at police brutality. They were blocked by the RUC and another counter-demonstration organised by Paisley, who was fast become an imposing and divisive presence in Northern Irish politics. A four-hour sit-down protest ensued.

It was against this backdrop of protest and counter-protest that the march in Armagh took place. I went to the assembly point early with a couple of friends and we attached ourselves to a group containing some older lads from school. They had congregated beneath a large red-and-black banner, which we soon discovered belonged to a small, but vociferous, local anarchist group. Ahead of them was a much bigger group of young radicals who belonged to the People’s Democracy party. They exuded a collective confidence that was in contrast to the more tentative demeanor of some of the older people there. As we set off towards the centre of town, the crowd sang We Shall Overcome. It is my recollection that the anarchists and student radicals didn’t join in, instead chanting “Ho Ho Ho Chi Minh! – We shall fight and we shall win!” and “Two, four, six, eight – organise and smash the state!” It was all very new and exciting, an event of almost epic proportions for those of us who had never witnessed such an energising disruption of the everyday.

On we went, singing and chanting, until the march came to an abrupt halt. In the ensuing confusion, my friends and I negotiated our way through the throng to the corner of Thomas Street, which led to the town centre. A line of uneasy-looking RUC men stood in front of their vehicles, which blocked the street. Beyond them, at the other end of the street, another row of police was visible, and behind them a huge crowd of union jack-waving loyalists. They were “the Paisleyites” and they had somehow been allowed to commandeer the centre of town. The protesters were outraged, but the presence of the Paisleyites was not entirely unexpected: rumours had circulated though the Catholic housing estates earlier that a certain Protestant shopkeeper had been seen handing out pickaxe handles to a mob that had arrived in town the night before. There were indeed large sticks being brandished in Market Street alongside the union flags being waved.

The Armagh march on 30 November 1968. Photograph: Ulster Gazette

Another rumour quickly spread through the marchers that some in the loyalist mob were armed. The tone of the march changed quickly from celebratory to defiant. An RUC man addressed the crowd who, surprisingly, listened attentively. He assured us that we were not allowed to proceed for our own security, which elicited hoots of jeering laughter. Prominent civil rights figures Ivan Cooper and John Hume cautioned restraint through a crackling megaphone. Their pleas were successful and, after some debate and a few attempts by one boy to scale the police barricade, the marchers turned back, much to the disgust of the young militants.

Later that day, police attacked a crowd of locals who had broken the windows of a departing bus full of Paisleyites. “I vividly remember the RUC arrived and the stewards tried to negotiate with them,” recalls Dermot Kelly, who attended the march as a young People’s Democracy activist. “It seemed to work, but then the RUC broke though their ranks and started batoning everyone in sight, including the moderators. It was vicious and indiscriminate.” A familiar narrative was being played out: loyalist triumphalism, aggressive policing of the protests, rising frustration among the protesters.

For days afterwards, the question asked by the nationalist community in Armagh was: what would have happened if a nationalist mob had attempted to take control of the town centre to prevent a loyalist march? It was, of course, a rhetorical question: everyone knew the answer. It was clear too, that a sizable minority of the protesters were growing impatient with the perceived compliance of the civil rights association in the face of the police and loyalist tactics. Where I lived, the middle-class representatives of Nicra were now being referred to derisively as “green Tories”.

What happened next, as 1968 gave way to 1969, and the schism between the moderates and the militants in the civil rights movement deepened, is viewed by some historians, including Paul Bew, as one of the crucial moments in the escalating drama that preceded the coming years of violence. On Monday 9 December 1968, the Northern Ireland prime minister, Terence O’Neill, made a television appeal to moderates of every political persuasion in what became known as his “Ulster stands at the crossroads” speech. It could be said, with hindsight, that the patrician and undoubtedly sincere O’Neill fundamentally misunderstood the depth of feeling on both sides, most crucially among the more hardline unionist forces that would soon topple him.

Bew sees it differently. “One could view the events of early 1969 as the real lost moment,” he says. “O’Neill had come up with a modest reform programme that many on the unionist side, as well as the Catholic middle class and the church, had accepted as a step forward and a meaningful commitment to further change. Our march shattered the prospects of that change taking place.”

The march Bew refers to was organised by the People’s Democracy party, of which he was then a member, against the advice of the civil rights association, who thought its route too provocative. Modelled directly on Martin Luther King’s Selma to Montgomery march from 1965, it began in Belfast on New Year’s Day, 1969, and ended four days later in Derry, its route taking the marchers through several rural Protestant areas along the way. For Michael Farrell and the party’s other young socialists it was a way of keeping the momentum of protest going in the face of reforms that they, like many in the nationalist community, thought of as too little too late.

In April 1969 21-year-old Bernadette Devlin became Britain’s youngest ever female MP, winning south Derry for the People’s Democracy party. Photograph: PA Archive/PA Images

About 40 student protesters left Belfast, growing to about 200 over the following days. They were attacked by stone-throwing loyalists on several occasions, but nothing prepared them for what happened as they crossed Burntollet Bridge on the fourth day. Waiting in ambush was a crowd of about 200 loyalists, including off-duty members of the “B-Specials” (an all-Protestant auxiliary police force), who descended on the marchers with sticks, iron bars, bottles and stones. Panic ensued with protesters, including several injured women, running into the river and the nearby fields. Though 80 RUC officers had accompanied the march, they seemed unable or unwilling to provide protection. The Burntollet ambush, shown on television that evening, was etched on the nationalist psyche as another example of state collusion with loyalist mob rule. “No one did as much damage to the unionist cause as the people who attacked the marchers at Burntollet,” says Bew.

In the months after, events in Northern Ireland accelerated. In early February, O’Neill announced the dissolution of Stormont and a subsequent election that would signal a major schism in the unionist party. On 17 April 1969, Bernadette Devlin stood as an independent Unity candidate in Mid Ulster. Aged 21, she became the youngest woman to be elected as an MP at Westminster and made her debut with one of the most stirring speeches ever made in the House.

A few days later, serious rioting broke out in Derry after clashes between civil rights protesters and loyalists, who laid siege to the nationalist Bogside area. The following month, what came to be known as the Battle of the Bogside took place when RUC officers and loyalists once again attempted to enter the area. They were met with fierce resistance from locals, many of whom had been present when the police attacked the civil rights march on Duke Street less than a year before. As Bogside residents forced the RUC out of the area and declared it Free Derry, rioting spread across Northern Ireland. The most vicious outbreak of sectarian violence erupted in Belfast, where hundreds of families were driven from their burning homes by a large loyalist mob, an event that directly led to the IRA re-forming and recruiting younger volunteers in nationalist areas. In Divis flats, a nine-year-old boy, Patrick Rooney, became the first child victim of the trouble, killed by RUC machine-gun fire as he lay sleeping. On Thursday 14 August 1969, British troops were deployed on the streets of Northern Ireland. The darkness had descended with a vengeance.

Derry youths throw petrol bombs at the RUC during the Battle of the Bogside in August 1969. Photograph: Peter Ferraz/Getty Images

That same evening, in Armagh, a local man called John Gallagher was shot dead by members of the B-Specials on the Cathedral Road. He was the first of eight people to die by violence that month, five of them killed by security forces. Gallagher had unwittingly walked into a street disturbance that followed the cancellation of a civil rights meeting in Armagh city hall due to the escalating tension. I remember the utter bewilderment felt by many in the town when news of his death spread. Already, the carnival atmosphere that had prevailed on the day of the civil rights march just nine months previously had become a distant memory.

There are those that still maintain that the people who took to the streets in peaceful protest share the blame for starting the Troubles. I, as you might have guessed, am not one of them. I leave the last word to someone from my home town who also marched on that day. “It seems to me now that we were idealistic to the point of naive in underestimating how violent the state’s response would be,” says Dermot Kelly. “But looking back, we were very clear in our aims. People have the right to aspire to equality in a democracy. You either believe that or you don’t. And, if you do, then marching for the rights denied you by a so-called democracy seems a perfectly reasonable thing to do.”

The Lost Moment exhibtion opens at the Nerve Centre, Derry on 28 April