President Trump's "America First" policy represents advancing U.S. interests abroad and facilitating cooperation with allies, National Security Adviser Gen. H.R. McMaster and National Economic Council Director Gary Cohn explained in an opinion piece Tuesday.

Writing in the Wall Street Journal, the two argued that the world shouldn't be perceived as a "global community."

"The president embarked on his first foreign trip with a clear-eyed outlook that the world is not a 'global community' but an arena where nations, nongovernmental actors and businesses engage and compete for advantage," Cohn and McMaster wrote.

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They said that the president's first foreign trip last week demonstrated his "America First" approach.

"America will not lead from behind. This administration will restore confidence in American leadership as we serve the American people," they said. "America First does not mean America alone. It is a commitment to protecting and advancing our vital interests while also fostering cooperation and strengthening relationships with our allies and partners. A determination to stand up for our people and our way of life deepens our friends' respect for America."

McMaster and Cohn said that the primary interest for the U.S. is the "safety and security of our citizens." They listed various actions the president took during his trip that exemplify this strategy. This includes Mr. Trump's "strong stand against terrorism" in Saudi Arabia, the $110 billion arms deal with the Kingdom, "reconfirming" America's commitment to NATO and Article 5 and the affirmation that Israel remains a democratic Jewish state.

"America First signals the restoration of American leadership and our government's traditional role overseas—to use the diplomatic, economic and military resources of the U.S. to enhance American security, promote American prosperity, and extend American influence around the world," they said.

Mr. Trump spoke about an "America First" approach during the 2016 presidential campaign. In an interview with The New York Times in March 2016, he said, "I'm not isolationist, but I am 'America First.' So I like the expression. I'm 'America First,'" Trump said. "We have been disrespected, mocked and ripped off for many, many years by people that were smarter, shrewder, tougher. We were the big bully, but we were not smartly led."

After he returned to the U.S., German Chancellor Angela Merkel appeared to rebuke Mr. Trump in remarks on Sunday in which she urged the European Union to stick together in the face of weakening U.S. support.

"The times in which we can fully count on others are somewhat over, as I have experienced in the past few days," Merkel said at a campaign event in a Bavarian beer tent with Bavarian governor Horst Seehofer. "And so all I can say is that we Europeans must really take our destiny into our own hands."

During his first foreign trip as president, Mr. Trump reportedly said at the summit that "the Germans are bad, very bad," according to meeting participants, quoted by Der Spiegel. On Friday, White House adviser Gary Cohn sought to clarify the criticism. The president also on Tuesday tweeted about the U.S. trade deficit with Germany and criticized Germany over its NATO payments.

We have a MASSIVE trade deficit with Germany, plus they pay FAR LESS than they should on NATO & military. Very bad for U.S. This will change — Donald J. Trump (@realDonaldTrump) May 30, 2017

Ultimately, McMaster and Cohn wrote, "those societies that share our interests will find no friend more steadfast than the United States. Those that choose to challenge our interests will encounter the firmest resolve."