James Mattis has resigned after the US's pullout from Syria.

https://www.theguardian.com/us-news/2018/dec/21/james-mattis-resignation-trump-erdogan-phone-call

The resignation of US defence secretary, James Mattis, was a surprise indeed because it was a protest against Trump's pullout from Syria.

Unbeknownst to Mattis, Trump reached a secret pact with Turkey for patriot missiles purchase in exchange for the US pullout as Turkey wanted to invade Syria to exterminate the Kurds.

http://sg-stock.blogspot.com/2018/12/the-truth-behind-uss-pullout-from-syria.html