On 11 September 2001 , 53 Army civilians ( 47 employees and six contractors ) and 22 soldiers were among the 125 victims killed in the Pentagon in a terrorist attack when American Airlines Flight 77 commandeered by five Al-Qaeda hijackers slammed into the western side of the building , as part of the September 11 attacks . In response to the 11 September attacks and as part of the Global War on Terror , U.S. and NATO forces invaded Afghanistan in October 2001 , displacing the Taliban government . The U.S. Army also led the combined U.S. and allied invasion of Iraq in 2003 ; it served as the primary source for ground forces with its ability to sustain short and long-term deployment operations . In the following years , the mission changed from conflict between regular militaries to counterinsurgency , resulting in the deaths of more than 4,000 U.S. service members ( as of March 2008 ) and injuries to thousands more . 23,813 insurgents were killed in Iraq between 2003 – 2011
American Airlines Flight 77
American Airlines Flight 77
United States Army