The Queen has said that "reconciliation, equality and mutual understanding" in Northern Ireland "cannot be taken for granted", in a message released to mark what many consider to be the country’s centenary.
She said "continued peace" in Northern Ireland "is a credit to its people, upon whose shoulders the future rests".
Her Majesty said the 100th anniversary of the Government of Ireland Act coming into effect was a "significant centenary" and one that "reminds us of our complex history, and provides an opportunity to reflect on our togetherness and our diversity".
"The political progress in Northern Ireland and the peace process is rightly credited to a generation of leaders who had the vision and courage to put reconciliation before division," the Queen said in her message.
"But above all, the continued peace is a credit to its people, upon whose shoulders the future rests.
"It is clear that reconciliation, equality and mutual understanding cannot be taken for granted, and will require sustained fortitude and commitment.
"During my many visits to Northern Ireland, I have seen these qualities in abundance, and look forward to seeing them again on future occasions."
The monarch said she looked back with "fondness" on her visit to Ireland with Prince Philip 10 years ago, adding: "I treasure my many memories, and the spirit of goodwill I saw at first hand.
"Across generations, the people of Northern Ireland are choosing to build an inclusive, prosperous, and hopeful society, strengthened by the gains of the peace process. May this be our guiding thread in the coming years."
In his own message to mark the milestone, Prime Minister Boris Johnson said: "People from all parts of Northern Ireland, the Republic of Ireland, the United Kingdom and across the globe, will approach this anniversary in different ways, with differing perspectives.
"While this is a moment of shared reflection, it is also an important opportunity to come together to celebrate Northern Ireland and build towards a better and even brighter future for all its people."
The PM added that the UK government would keep on showcasing "all the brilliant things" that Northern Ireland contributes to the rest of the UK.
Northern Ireland was created on this day 100 years ago when the Government of Ireland Act came into effect and the island of Ireland was partitioned.
The 32 counties of Ireland were split into two – with Antrim, Armagh, Derry, Down, Fermanagh and Tyrone forming Northern Ireland and the rest making up what would soon become the Irish Free State and much later the Republic.
But there are differing opinions on when exactly Northern Ireland was created, with some pointing to other points in history for the country’s foundation.