It is noted that he expressed his position in a letter that NBC television published on his Twitter page.

It clarifies that the head of the Pentagon decided to resign so that the American leader Donald Trump could find the Minister of Defense with more similar views.

“Since you have the right to have a minister of defense, who has more similar views to yours ... I think I have the right to resign from my position,” he said

Defense Sec. Mattis resignation letter:

"I hope you’re losing your peace of mind ... pic.twitter.com/HqkGDp7kBJ

- NBC News (@NBCNews) December 20, 2018

Mattis in his letter stressed that the United States will not be able to protect its interests without maintaining strong allied relations and "showing respect for allies."

Earlier, Trump announced that Mattis will retire at the end of February 2019.