LONDON (AP) — Northern Ireland marked what is widely considered to be its centenary on Monday, with Queen Elizabeth II stressing the need for “reconciliation, equality and mutual understanding” as she sent her “warmest good wishes” to its people.

U.S. Secretary of State Antony Blinken, on a visit to London, said the U.S. will continue to encourage the U.K. and the European Union “to prioritize political and economic stability in Northern Ireland” as they work through their post-Brexit relationship.

Northern Ireland was created on May 3, 1921, when the Government of Ireland Act came into effect and partitioned the island of Ireland into two separate entities. Northern Ireland became part of the U.K. alongside England, Scotland and Wales, while Ireland would later that year become what was then known as the Irish Free State.

Much like the day that Northern Ireland was founded 100 years ago, there were no huge celebrations or grand ceremonies Monday, given the sharply differing views on its creation and subsequent history. Restrictions related to the coronavirus pandemic have also led to all commemorations this year being scaled back.

Since its creation, Northern Ireland society has been split between those who want to remain in the U.K. and those who wish to see Northern Ireland become part of the Republic of Ireland. For decades, that fissure fueled sectarian violence: the so-called Troubles, which resulted in around 3,500 deaths.

The Good Friday Agreement of 1998 formalized power-sharing arrangements between unionists and nationalists. It's not always been a smooth process politically, with the two sides often unable to reach agreement on how to govern, and there's been sporadic outbreaks of violence.

“This anniversary reminds us of our complex history, and provides an opportunity to reflect on our togetherness and our diversity,” the queen said in a statement.

“It is clear that reconciliation, equality and mutual understanding cannot be taken for granted, and will require sustained fortitude and commitment," she added.

The queen also referred to “treasured” memories she shared in Northern Ireland with her late husband, Prince Philip, who died last month at 99.

British Prime Minister Boris Johnson also marked the date, describing it as a “very significant" anniversary and stressed the importance of reflecting on the “complex history” of the past 100 years.

"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,” he said.

In recent weeks, there have been outbreaks of violence across Northern Ireland, with the unionist community particularly aghast at post-Brexit trade rules that took effect this year. These imposed customs checks on some goods moving between Northern Ireland and the rest of the U.K., which did not exist when the U.K. was part of the EU.

Blinken urged all politicians and parties to prioritize peace and stability.

“The United States remains a steadfast supporter of a secure and prosperous Northern Ireland, in which all communities have a voice and can enjoy the gains of the hard-won peace," he told reporters on Monday.

Although no major celebrations were held, plans to mark the centenary this year included tree-planting projects. Every school was given a native tree to plant in their grounds and many will explore what the future will look like in the next 100 years.

“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,” the queen said. “May this be our guiding thread in the coming years.”