WASHINGTON — King Charles III used a historic address at the U.S. Capitol on Tuesday to salute the relationship between America and the United Kingdom while cautioning that past achievements alone cannot be expected to sustain it. 

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King Charles III used an historic address at the U.S. Capitol Tuesday to salute the relationship between America and the United Kingdom while cautioning that past achievements alone cannot be expected to sustain it

Charles’ speech made him just the second British monarch to address a joint meeting of Congress, which is considered a relatively rare honor bestowed upon major world figures; The first was his mother, Queen Elizabeth II, who spoke in the chamber in 1991

Hanging over the king’s address and trip to the U.S. is the recent strains between Trump and fellow leaders of European and NATO member countries, which he contends have not done enough to aid the U.S. in his war effort in Iran

Speaking in the U.S. House chamber filled with members of Congress, Charles paid tribute to the alliance between the two nations that he noted was built over the centuries.

“The bond of kinship and identity between America and the United Kingdom is priceless and eternal,” said Charles. “It is irreplaceable and unbreakable.”

He gave a particular nod to America’s Founding Fathers — as the trip is meant to help commemorate the 250th anniversary of the country this year — calling them “bold and imaginative rebels with a cause.” And he noted that, as a result, the U.S.-U.K. partnership was “born out of dispute” but, nonetheless, was “no less strong for it.”

But Charles also used the speech to address the uncertainty and “immense challenges” currently facing the world and he appeared to come equipped with the message that both the U.S. and U.K., which have recently seen tensions bubble, will need to work to foster the relationship for the future. 

“In this unpredictable environment, our allowance cannot rest on past achievements or assume that foundational principles simply endure,” Charles said. 

He went on to reference a recent comment from British Prime Minister Keir Starmer calling the partnership “indispensable” to argue that the two nations “must not disregard everything that has sustained us for the last 80 years. Instead, we must build on it.”

Charles’ speech made him just the second British monarch to address a joint meeting of Congress, which is considered a relatively rare honor bestowed upon major world figures. The first was his mother, Queen Elizabeth II, who spoke to Congress in 1991.

The king referenced his mother’s address to make the case that, in many ways, the world today is “more volatile and more dangerous” than it was when she gave her own speech there. He argued that the “challenges we face are too great for any one nation to bear alone.”

Hanging over the king’s address and trip to the U.S. is the recent strains between Trump and fellow leaders of European and NATO member countries, which he contends have not done enough to aid the U.S. in his war effort in Iran. The president has frequently claimed that NATO countries have shown they will not be there for the U.S. and has escalated his talk of potentially pulling America out of the alliance. He has also feuded with Starmer particularly over the use of military bases, but offered a strong backing of the U.S.-U.K. relationship when he welcomed Charles to the White House on Tuesday morning. 

In what could be seen as a reference to it all, the king in his speech noted that the only time NATO’s Article 5 clause regarding collective defense has been invoked was to assist the U.S. following the attacks on 9/11.

“We stood with you then, and we stand with you now, in solemn remembrance of a day that shall never be forgotten,” he said. 

Charles also used the reference to argue that the same support should be afforded to Ukraine amid the war with Russia in the country. That comes as Trump and many of his GOP allies in Congress have leveled criticism about the amount of money the U.S. has spent to support Ukraine, often citing the president’s “America First” foreign policy agenda. 

And more broadly, the king called for resisting “the clarion calls to become ever more inward looking” as he went on to note the importance of America’s actions on the world stage. 

“America’s words carry weight and meaning as they have since independence,” he said. “The actions of this great nation matter even more.”

The speech came on the second day of he and his wife, Queen Camilla’s four-day trip to the U.S., which will also see the royal couple travel to New York and Virginia. 

Charles kicked off the day taking part in Trump’s formal arrival ceremony for the king held on the White House South Lawn Tuesday morning. The king and queen are set to return to the White House in the evening for more pageantry and a formal state dinner.