Former Defense Secretary Mattis Urges U.S. To Work With Allies

In an excerpt from his book published in the Wall Street Journal, Mattis discusses his concerns about the Trump administration, focusing on the threat of tribalism in the US. He emphasizes the importance of maintaining strong alliances, using a Marine saying to illustrate his point. Mattis subtly criticizes Trump's foreign policy, particularly regarding disputes with allies and the withdrawal of US troops from Syria, which led to his resignation.

What criticism does Mattis imply regarding his former boss?

What event led to Mattis's resignation from the Department of Defense?