Today, Britain First Northern Ireland (BFNI) and unionists across the province are commemorating the Battle of the Boyne.
It's a national holiday there, with street parties, marching bands and some of the world's biggest bonfires.
But why is a 300-year-old battle still so important?
The Battle of the Boyne began on July 1, 1690 across the River Boyne close to the town of Drogheda in the Kingdom of Ireland, which is the modern-day Republic of Ireland.
The battle took place between William of Orange and his uncle, James II.
William of Orange was a Dutch protestant who had recently been jointly crowned monarch of England, Scotland and Ireland during the 'Glorious Revolution'. ...
After William was crowned, James – [who] was also William's father-in-law - escaped to exile in France.
In France, at that time the greatest military power in Europe, catholic King Louis XIV supplied James with troops to head back to battle the protestant rule.
In 1689, James landed back in Ireland in the hope of regaining the English crown. ...
On June 14, William marched his forces - the largest Ireland had seen at that time, with more than 1,000 horses - south to James's stronghold near Dublin.
The ensuing battle at the River Boyne has come to be remembered as the final time two crowned kings of England, Scotland and Ireland met in battle.
William grazed his shoulder by a bullet early on, but as a veteran military leader, he had the strength of experience on his side.
By contrast, James was approaching sixty with his best years behind him, and after around four hours he gave the order to retreat.
William marched to Dublin in victory, and James returned to exile in France. ...
The battle marked a major turning point in protestant history. ...
For protestants in Ulster, the victory ensured the survival of the protestant, English-speaking areas.
The victory is still celebrated every July 12 in Northern Ireland by the Orange Order, named after William of Orange.