Former German Chancellor Angela Merkel argued President-elect Trump does not believe in “any win-win situation,” and it makes international collaboration difficult.

Merkel, who served as chancellor from 2005-21, has seen U.S. presidents come and go. In an interview with NPR, she detailed her new book, “Freedom: Memoirs 1954 – 2021,” and her 2017 meeting with Trump at the White House during his first term.

She wrote that she flew home from the meeting feeling uneasy.

“Donald Trump, as president, was a person who very strongly supported his ideas. That’s natural. That’s what every president of the United States of America does, as every chancellor does,” Merkel said. “But Donald Trump, less than others, believes in the capability or the quality of a compromise.”

“He wants to be the sole winner in any type of conflict, and he does not believe in any win-win situation where both sides benefit from a solution,” she continued. “And that makes the collaboration more difficult and different than other head of government.”

As Trump prepares to retake the White House, the international community is bracing for what changes may come.

The president-elect has said he could “end” the Russia-Ukraine war in one day and flexed his relationship with Russian President Vladimir Putin and North Korean leader Kim Jong Un.

There are also concerns that Trump could withdraw the U.S. from NATO. He’s questioned the alliance’s future and wants member countries to pay more in defense spending. In February, Trump said he would encourage Russia to do “whatever the hell they want” to members of the organization that didn’t pay up.

Several European countries have been bracing for a shift under Trump’s second term, but NATO Secretary-General Mark Rutte said he will work with the new administration.

Merkel said she hopes Trump will be able to see the true purpose of the alliance and noted that there are “good reasons” for the U.S. to want NATO to remain strong.

“I hope that President-elect Trump, as he did in his first term of office, now also understands that NATO does not only serve the purpose of protecting Europe, with the support of the U.S. and Canada, but that the partnership with Europe is also a benefit for the United States of America,” Merkel said.

She added that “together,” the 32 member countries are much stronger than their adversaries.