My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues, Mattis wrote in his resignation letter dated Thursday.
Because you have the right to have a secretary of defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position.
Mattis, who was confirmed by the Senate in January 2017, touted some of the progress DoD has made in the past couple of years to meet the National Defense Strategys goals such as building up force lethality and readiness and putting the Pentagon on a more sound budgetary footing.
His four-decade military career included time as head of U.S. Central Command, U.S. Joint Forces Command and NATOs Supreme Allied Command for Transformation.
He also served as commanding general of Marine Corps Combat Development Command and executive secretary to the defense secretary.
Mattis, a two-time Wash100 winner, is a former Davies Family Distinguished Visiting Fellow at Stanford Universitys Hoover Institution.