Secretary of Defense Jim Mattis talks with U.S. Army Lt. Gen. Stephen Townsend, then-commander of U.S troops in Iraq and Syria, during a flight in Iraq on Aug. 22.
North Korean leaders meet during the 8th Conference of Munitions Industry at the April 25 House of Culture in Pyongyang on December 14. (AFP/Getty Images)
Flanked by members of the U.S. military, President Donald Trump signs the National Defense Authorization Act on December 12. (Mark Wilson/Getty Images)