Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of " United States of Jihad: Investigating America's Homegrown Terrorists ."

(CNN) In picking Gen. Jim Mattis for Defense secretary, President-elect Donald Trump has said that he found his "Gen. George Patton." Yet that label may not really capture what makes Mattis a distinctive choice. Mattis has been sharply critical of President Barack Obama's policies on Iran, and Obama's capping of troop numbers and campaign end-dates in theaters of war such as Afghanistan and Iraq. Mattis also appears to be a skeptic of the Obama-era policy of putting women into combat roles.

Mattis, 66, is a storied retired Marine general beloved by his troops whose skeptical views on Iran and appetite for a robust military that is unencumbered by political correctness align closely with those of his new boss. But Mattis is also a warrior-intellectual who easily and unpretentiously quotes both the Roman stoic Marcus Aurelius and Eliot Cohen, the Republican military strategist who was a leader of the "never Trump" movement.

An American four-star general is likely to move around some two dozen times during the course of a long career. Typically, the general will move his family and household effects from one posting to the next. Mattis, who is unmarried, instead moved his books -- all 7,000 of them -- many of which, he has since given away to libraries.

A student of warfare

In 2003 during the Iraq War, Mattis cited Alexander the Great when he explained in an email to a fellow officer why deep reading about the history of warfare can help to save American lives on the battlefield: "By reading, you learn through others' experience, generally a better way to do business, especially in our line of work where the consequences of incompetence are so final for young men."

Mattis may be nicknamed "Mad Dog" because of his ferocity on the battlefield and his colorful aphorisms — "Be polite, be professional, but have a plan to kill everybody you meet" -- but not only is he an avid reader, he is also a deep thinker.

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He co-authored with General David Petraeus the 2006 counterinsurgency manual that helped to revolutionize the US approach to the Iraq War, emphasizing that fighting insurgents required -- at least in the short term -- assuming greater risks for American troops who had to get out of their massive bases and live among the Iraqi people if they were to have a chance of really understanding and ultimately defeating the Iraqi insurgency.

In August, Mattis published -- together with military historian Kori Schake -- an edited volume about American civilian-military relations, "Warriors and Citizens," that surely many folks at the Pentagon will be reading in coming weeks as they try to understand Mattis and where he will likely be driving "the building," as the Pentagon is known to its many inhabitants.

His views on politics and war

In their concluding essay , in which Mattis and Schake variously quote the jurist Oliver Wendell Holmes; the novelist Phil Klay; founding father Samuel Adams and the Roman poet Juvenal, they make several key observations:

First, since 9/11, American political leaders such as Presidents George W. Bush and Barack Obama have deputized military leaders to make the political case for America's wars. Bush left it to General David Petraeus to make the case to Congress and the American people that the 2007 "surge" of US troops into Iraq was turning the tide of the war. President Obama, in Mattis' telling, "has been mostly silent on the war in Afghanistan since 2009; the case for continuing American troop presence has been made entirely by the military."

Mattis clearly regards the policy of leaving it to military leaders to make the case for America's war as dangerous. Elected officials have a responsibility, according to Mattis, "to win political arguments instead of depending on the military to do so."

Second, Mattis writes that the US is at a disadvantage because America's enemies are fighting "total war" while the United States is fighting "only limited wars."

Third, because of the current deference that the public and politicians have to the military and to veterans, the defense budget is getting dangerously skewed "toward pay and benefits to the detriment of training, equipment and numbers in the force." Mattis and Schake cite a statistic that in less than a decade, 80% of the US Army's spending could be devoted just to personnel costs.

Fourth, they are critical of using the military for the kind of social experimentation that undermines, in their view, military readiness: "Public debates allowing open homosexuals to serve and opening combat assignments to women show civilian attitudes strongly at variance with the military (especially those serving in ground combat units where the atavistic nature of warfare is most pronounced.)"

Fifth, that an overemphasis on the casualties of war, and PTSD and military suicides among veterans has created a culture of "victimization" around the military. Mattis and Schake say that Obama was more likely to visit Bethesda Naval Hospital to visit the wounded than to visit the massive army at Fort Hood, Texas, sending "a cultural message that casualties are more important than what we are fighting for."

Sixth, that America's post-9/11 wars in Afghanistan and Iraq "lacked clear political objectives and carried self-imposed limitations such as troop caps, campaign end-dates disconnected from conditions on the ground and restrictions on using ground troops at all (or that allowed them only in incremental numbers)."

How he meshes with Trump

Overall, Mattis and Schake urge that political leaders such as Trump should be making the case for the necessity of America's wars rather than relying on the military to do so; that those wars should be better resourced; the United States should be in those wars to win, and the military should focus on waging successful wars rather than being a petri dish for social experimentation.

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It's very much of a piece with Trump's "America First" sloganeering, but Mattis lays out this thinking with much greater specificity than his new boss.

Further clues about how Mattis may guide the Pentagon can be found in a thesis entitled "The Mattis Way of War" written by Maj. Michael Valenti while he was a student at the US Army Staff College. The thesis examined how Mattis commanded what The Military Times describes as "the deepest insertion of Marines into a combat zone in US history." In the months after 9/11, Mattis led 1,000 Marines who seized an abandoned airfield behind enemy lines in the heart of Taliban-controlled Afghanistan in Kandahar province.

The thesis, which was published in September, also examines how then-Maj. Gen. Mattis led the First Marine division during the invasion of Iraq in 2003. The thesis makes a number of important observations about Mattis' leadership style.

First, Mattis tried to keep his staff as small as possible to increase the speed of his operations. Influenced by the work of leadership guru Jim Collins, he focuses "on getting the right people on board" in his organization and "getting the wrong people out."

Second, Mattis understands that history doesn't repeat itself, but "it can lay the cognitive framework for innovative solutions to complex problems." When Mattis designed the operation to insert the Marine force in Afghanistan, Mattis was informed by similar raids conducted during World War II and even the American Civil War in which troops were inserted behind enemy lines to "destroy the enemy's security and shatter his will."

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Similarly, when Mattis prepared for the invasion of Iraq he "mandated that every major and above in the division read Russell Braddon's 'The Siege,'" which was one of the only books ever written about fighting a war in Iraq. It chronicled the British fight there during World War I.

Third, Mattis issued very clear "commander's intent" guidelines so that all his Marines understood the purpose and goals of the fight they were embarking upon.

Fourth, he pushed the responsibility for decision-making during the battles he led down to the lowest levels possible.

So what do Mattis' views and history as a military leader suggest about how he might help to shape policy in the Trump administration?

A greater troop presence?

Clearly, an urgent priority will be what to do about Afghanistan where the Taliban now control or contest territory in which 10 million Afghans live and where ISIS has established a foothold. The Obama administration has signaled that US troops will eventually be pulling out of Afghanistan since as early as December 2009 when Obama first announced a surge of US troops into the country, but also announced their withdrawal date.

Mattis clearly finds this deeply unsatisfactory and we can expect him to push for a more robust troop presence in Afghanistan unconstrained by arbitrary pullout deadlines.

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Similarly, Mattis is not a fan of Obama's incremental troop deployments in Iraq and Syria to defeat ISIS. Based on what he has said in the past, we should expect that he would push for whatever number of troops are needed to get the job done.

Based on Mattis' comments about the role of women in combat, we might see a Mattis-run Pentagon not placing women into combat roles in contrast to the present policy.

In a speech in Washington in April, Mattis said that Iran is "the single most enduring threat to stability and peace in the Middle East." This view is shared by Trump's designated national security adviser, Lt. Gen. Michael Flynn, and his nominee for CIA director, Rep. Mike Pompeo, R-Kansas. We can expect this troika will push for tougher action on Iran, though Mattis is also on record as saying that there is "no going back" on the Iran nuclear deal, which puts him out of step with some in Trump's inner circle.

Already, Mattis seems to have influenced Trump to at least consider the idea that returning to an era when torture was employed by US officials is counterproductive.

If Mattis is confirmed as secretary of defense -- which will require a congressional waiver since he recently retired as a military officer -- he can be expected to argue for a robust military; a deep commitment to America's wars; a skepticism about putting women on the front lines, and an adherence to the Geneva Conventions when it comes to the treatment of captured American enemies.