Secretary of Defense James Mattis after a NATO defense ministers meeting in Brussels. Thomson Reuters

Defense Secretary Jim Mattis just gave the most wide-ranging, profoundly thoughtful interview of his tenure so far as Pentagon chief, touching on the country's deep political divide, the fundamental nature of war, the role of the diplomacy, the value of education in defeating ideology, the lessons of history, the similarities between the administrations of Obama and Trump, and the power of the individual to effect change.

And he gave it to a high school journalism student in Mercer Island, a Seattle suburb.

Mattis agreed to speak by phone with Teddy Fischer, after the teenager sent a text requesting an interview to Mattis' private number, which was inadvertently disclosed in a photograph published in the Washington Post in May.

The interview, conducted on Memorial Day, was only scheduled to go few minutes, but lasted about 45 minutes, and resulted in some of Mattis' more insightful ruminations on the current challenges he faces.

Among his observations: the need for the State Department, not the Pentagon, to be in charge of war.

"What you have to do is make certain that your foreign policy is led by the diplomats, not by the military," Mattis said.

"The way that you get your diplomats listened to in an imperfect world is you make certain you back them up with hard power. The reason I say that is, as much as I'd like to live in a world where people who are out to do others harm would be willing to listen to rational thought, not everyone is."

Secretary of Defense James Mattis walks past saluting cadets as he arrives for commencement ceremonies at the US Military Academy in West Point, New York, May 27, 2017. Thomson Reuters

The interview is sprinkled with some new, and recycled Mattisisms, such as, "I don't care for ideological people. It's like those people just want to stop thinking," and "If you can help the larger community in the world, you won't be lying on a psychiatrist's couch when you're 45 years old wondering what you did with your life."

He also offered some surprising insight into how he thinks about strategy. For instance, he doesn't see a lot of difference between President Trump's strategy for defeating terrorism and President Obama's.

"I think the two administrations are more variations on a theme than they are dramatically different approaches," Mattis said, but also suggests Obama would have done better to listen to his Secretary of State Hillary Clinton, who advocated more aggressive intervention in Syria.

And on Syria, Mattis places the blame for hundred of thousands of deaths squarely on Iran and Russia who have propped up Syrian leader Bashar Assad.

President Donald Trump shares a laugh with Defense Secretary Jim Mattis, center, and Commerce Secretary Wilbur Ross as he meets with his Cabinet at the White House in Washington, March 13, 2017. AP Photo/Andrew Harnik

"The only reason that Assad is still in power is Russia's diplomatic veto, Iran's military power, and now Russia's military power," Mattis said. "Without those two, the Syrian people would have run him out five years ago."

And Mattis still believes Iran is by far the biggest threat to peace and stability in the region, and he gave credit again to Hillary Clinton effectively using economic sanctions, forcing the Iranian regime to the negotiating table.

"This is a regime that employs surrogates, like Lebanese Hezbollah to threaten Israel, to murder the former Lebanese prime minister, murder Israeli tourists in Bulgaria," Mattis said. "They tried to murder an Arab ambassador in downtown Washington D.C."

And he suggested the Iran nuclear deal, which President Trump has disparaged, may buy some time.

"You can see why President Obama was so anxious to try to block them on getting a nuclear weapon."

And in providing advice to young Fischer, Mattis the scholar-warrior returned often to one his favorite themes, the lessons of history, and what they tell us about today.

"The human condition, the aspirations, the dreams, the problems that are associated with being social animals, not being a hermit and living alone, but having to interact with others, whether it be your local school district, your community, your state, your county, your national, your international relations, history will show you not all the answers, but it'll tell you a lot of the questions to ask and furthermore, it will show you how other people have dealt successfully or unsuccessfully with similar type issues," he said.

Defense Secretary James Mattis and Joint Chiefs Chairman Marine Gen. Joseph Dunford hold a briefing on the campaign to defeat ISIS, May 19, 2017. Thomson Reuters

And while Mattis lamented the tendency of people these days to demonize their political opposites, he suggested history would show that's nothing new for America.

"If you study history, you realize that our country has been through worse and here's how they've found their way through that," Mattis said. "You lose your paralysis, you lose your, I would almost call it unproductive worry, and you replace it with productive action."

His advice: be slow to characterize your fellow Americans. "They're human beings too. There's no reason to get all worked up as if someone is evil or crazy."

"I think the way you get over it is, you take people one at a time and you give them the same credit you give yourself and your ideas."

The full interview can be read here.

And why did he give the interview to a teenage high school student from Washington state?

"I was going through listening to the messages and deleting them. But you're from Washington state," Mattis told Fischer. "I grew up in Washington state on the other side of the mountains there on the Columbia River. I just thought I'd give you a call."