A young girl watches a loyalist marching band parade through west Belfast on Saturday.

'It's two steps forward, 10 steps back:' Brexit, shifting demographics and familiar tensions stoke divisions in Northern Ireland

Updated 1357 GMT (2157 HKT) July 11, 2021

Belfast, Northern Ireland (CNN)Niamh Burns is organizing a special 20-year reunion for her schoolmates this year. But while the accomplishments of the "Courageous Classes of 2001" are worth celebrating, the date they are commemorating is not.

Over the course of 12 weeks in 2001, Burns and the other pupils at north Belfast's Holy Cross Girls' primary were subjected to a barrage of abuse from a group of loyalist Protestants blocking their path to the school gate.
The unrest, reported on globally at the time, began during the last week of the summer term, before violence exploded on the children's return to school in the fall. An angry mob threw urine-filled balloons and, eventually, a pipe bomb as children -- some as young as five -- ran the gauntlet each day to get to class.
It had been three years since the signing of the Good Friday Agreement, the landmark peace accord also called the Belfast Agreement that marked an end to the decades-long conflict known as the Troubles, but sectarian tensions were still rife in Belfast's Ardoyne neighborhood.
Two decades later, violence is still never far from the surface in Northern Ireland, with the pain of the past still driving discontent.
As July 12 nears, and loyalist Protestants prepare the annual celebration of King William of Orange's victory over Catholic King James II at the Battle of the Boyne in 1690 with marches and bonfires, there are fears that unrest could spill onto the streets, as they did briefly earlier this year.
The catalyst for the chaos at Holy Cross in 2001 is still disputed: Protestant loyalists, who identify as British, say Catholic nationalists, who identify as Irish, had knocked a loyalist off a ladder as he was hanging a flag ahead of the traditional loyalist marching season. Catholic nationalists say it was an attack on their presence in a majority-Protestant area.
But underscoring all of this was a bigger issue: While the Catholic Ardoyne was thriving, a Protestant exodus from the neighboring enclave of Glenbryn was intensifying, with claims of intimidation leveled at nationalist republicans.
The Holy Cross dispute showed just how fragile the new peace was. Its continuing impact has added to a collective trauma that serves as a unifying thread across Northern Ireland.
The Holy Cross Girls Primary School, in north Belfast's Ardoyne area, became a flashpoint for sectarian violence in 2001.
While others have struggled to reconcile the past, years of therapy and cross-community engagement have helped some of the Holy Cross schoolgirls to move forward.
"You don't ever really overcome it, you just learn how to live with it," explains Burns, who was five when the protests erupted outside her school.
She and her older sister, a fellow pupil, experienced night terrors as a result of the violence, but despite everything, Burns says the school "was a safe place" -- life went on as normal once they were inside.
Burns, a cross-community worker, says her experiences at Holy Cross have shaped her life since -- in a largely positive way: "I've carried my experience with me the whole time, which has allowed me to do the work that I am doing now."
For Gemma McCabe, another former Holy Cross student, memories of the dispute are painful, but she says the incident hasn't defined her outlook.
"I