General Jim Mattis has been US Secretary of Defense for the past two years

US President Trump says he will nominate a replacement soon

From Mattis' resignation letter:

  • his core belief is that the US needs to maintain strong alliances and show respect to allies
  • is resigning so that President Trump can have US defence secretary with views more aligned with his
  • US must be unambiguous with nations like Russia and China

Full text:

Politely worded, but this is brutal from a well-respected official like Mattis.