Robert Gates becomes the new Secretary of Defense, replacing Donald H. Rumsfeld, who had served since January 2001. (It was Rumsfeld’s second tour in the post; he first served under President Gerald Ford from November 1975 to January 1977.)
The U.S. began extensive air and artillery strikes against Islamic State group targets in Syria on Dec. 19 in retaliation for the killing of three Americans on Dec. 13 by a gunman affiliated with ISIS, U.S. officials said.
