President Trump has effectively fired his Secretary of Defense Jim Mattis by announcing that Mattis, a four star Marine General and former CIC of US Central Command will be leaving his administration at the end of February.
https://edition.cnn.com/2018/12/20/politics/donald-trump-james-mattis-out/index.html
It is clear from his resignation letter, that General Mattis has been displaced because he is in fundamental disagreement with President Trump’s surprise announcement on Twitter that he intends to order a full and rapid withdrawal of all US forces from Syria.
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 wrote in his letter.
The departure of Mattis marks what is probably the most serious breach between a US President and his senior military commanders since President Truman fired General Douglas MacArthur for insubordination in April 1951 at the height of the Korean war.
Whereas General MacArthur was dismissed because he wanted to enlarge the Korean war by attacking China with nuclear weapons, Mattis has been forced out because he disagreed with President Trump’s self-confident assertion that ISIS are already defeated - A view shared by absolutely none of the relevant military experts in this field, nor by Trump’s own National Security Advisor John Bolton.
Meanwhile, Washington officials are said to be bracing for another announcement of a similar ilk on Afghanistan.
https://edition.cnn.com/2018/12/20/politics/trump-afghanistan-announcement/index.html