This 2015 file photo shows U.S. soldiers from Dragon Troop of the 3rd Cavalry Regiment discuss their mission during their first training exercise of the new year near operating base Gamberi in the Laghman province of Afghanistan. WASHINGTON – The Trump administration opened a new military front Thursday when it ordered dozens of cruise missiles against a Syrian air base, adding to a growing list of recent U.S. military forays. A look at where the United States has fought in the 21st century. After al-Qaida attacked the U.S. on Sept. 11, 2001, the U.S. led an invasion of Afghanistan that ousted the Taliban. Though the U.S. and NATO formally ended their combat mission in Afghanistan at the end of 2014, the war -- now in its 16th year -- drags on.