As a captain, he was assigned as the Naval Academy Preparatory School's Battalion Officer, commanded rifle and weapons companies in the 1st Marine Regiment, then served at Recruiting Station Portland, Oregon, as a major.

[44] In December 2001, an airstrike carried out by a B-52 bomber inadvertently targeted a position held by US special operations troops and Afghan militiamen in Uruzgan Province.

Numerous men were wounded in the incident, but Mattis repeatedly refused to dispatch helicopters from the nearby Camp Rhino to recover them, citing operational safety concerns.

[52] When asked by the press about footage on Arabic television of a child's body being lowered into a grave, he replied: "I have not seen the pictures but bad things happen in wars.

Believing that a need for restraint in war as key to defeating an insurgency, he added: "every time you wave at an Iraqi civilian, al-Qaeda rolls over in its grave.

[56][57][58][59][60] In the letter Mattis also encouraged his men to "fight with a happy heart," a phrase he attributes to Sitting Bull, and that he learned from the Native American oral tradition.

On September 28, 2007, the United States Senate confirmed Mattis's nomination, and he relinquished command of the I MEF on November 5, 2007, to Lieutenant General Samuel Helland.

[72] He lobbied the Obama administration for a more aggressive response to Iran, including more covert operations and disruption of Iranian arms shipments to Syria and Yemen.

[82][23] In December 2015, Mattis joined the advisory board[83] of Spirit of America, a 501(c)(3) nonprofit organization that provides assistance to support the safety and success of American service personnel and the local people they seek to help.

[85][86][87][88][89] Previously, in mid-2012, a Department of Defense official evaluating Theranos's blood-testing technology for the military initiated a formal inquiry with the Food and Drug Administration about the company's intent to distribute its tests without FDA clearance.

[96] The National Security Act of 1947 requires a seven-year waiting period before retired military personnel can assume the role of secretary of defense; Mattis's nomination meant that it was the first time since 1950 (in that instance for George Marshall) that a waiver of the law was needed.

[8] During a press conference in London on March 31, 2017, with the British secretary of state for defence, Michael Fallon, Mattis said North Korea was behaving "in a very reckless manner" and must be stopped.

[104] On June 3, Mattis said the United States regarded North Korea as "clear and present danger" during a speech at the international security conference in Singapore.

[105] In a June 12 written statement to the House Armed Services Committee Mattis said North Korea was the "most urgent and dangerous threat to peace and security".

[108] Mattis responded to critics who suggested the Trump administration had loosened the rules of engagement for the US military in Iraq after US-led coalition airstrikes in Mosul killed civilians,[109] saying, "We go out of our way to always do everything humanly possible to reduce the loss of life or injury among innocent people.

[113] The following day, Mattis gave his first Pentagon news conference since becoming secretary of defense, saying ISIL's defeat remained "our priority," and the Syrian government would pay a "very, very stiff price" for further usage of chemical weapons.

[119] On April 20, 2017, one week after the Nangarhar airstrike, Mattis told reporters that the US would not conduct a damage assessment "in terms of the number of people killed" in Afghanistan.

[121] On June 13, Mattis said US forces were "not winning" in Afghanistan and the administration would develop a new strategy by "mid-July" while speaking to the United States Senate Committee on Armed Services.

[122] On June 29, Mattis said the Obama administration "may have pulled our troops out too rapidly" and that he intended to submit a new Afghanistan strategy to Trump upon his return to Washington, D.C.[123] The United States has been openly arming the Syrian Kurdish fighters in the war against ISIL since May 2017.

[124] Following the start of the Turkish invasion of northern Syria aimed at ousting US-backed Syrian Kurds from the enclave of Afrin, Mattis said in January 2018: "Turkey is a NATO ally.

[127] In November 2018, the CIA assessed with "high confidence" that Saudi Arabia's Crown Prince Mohammad bin Salman ordered the assassination of Washington Post columnist Jamal Khashoggi.

[128] Under mounting pressure from lawmakers who wanted action against Saudi Arabia, Mattis and Secretary of State Mike Pompeo, in a rare closed briefing of the Senate, disputed the CIA's conclusion and declared there was no direct evidence linking the crown prince to Khashoggi's assassination.

[129] Wherever Mattis traveled overseas, he brought the Defense Security Cooperation Agency director (the official in charge of weapon sales to foreign governments), according to Lt. Gen. Charles Hooper, speaking at the Brookings Institution in June 2019.

Instead, Trump chose General Mark Milley, Army Chief of Staff, whom Mattis had recommended for the position of Supreme Allied Commander Europe.

Mattis also affirmed the need for "treating allies with respect and also being clear-eyed about both malign actors and strategic competitors" and remaining "resolute and unambiguous" against authoritarian states such as China and Russia.

[146] He changed his position after becoming "angry and appalled" about the events leading up to the violent treatment of noncombative protesters near the White House on June 1, 2020, for the purpose of a photo op for Trump at the church across Lafayette Square.

[148][149][150] Mattis, along with all other living former secretaries of defense, ten in total, published a Washington Post op-ed piece in January 2021 telling President Trump not to involve the military in determining the outcome of the 2020 elections.

[166] Speaking at a 2015 conference sponsored by The Heritage Foundation in Washington, D.C., Mattis said he believed that Russian President Vladimir Putin's intent is "to break NATO apart.

"[172] In 2017, Mattis said that budget cuts would hamper the ability to monitor the effects of global warming,[13] and noted, "climate change is a challenge that requires a broader, whole-of-government response.

Demonstrating unequivocal support and unwavering commitment to Canada, General Mattis has significantly strengthened Canadian-American relations and has been a critical enabler in both countries’ shared achievements in Afghanistan.