The United States suffered through the worst terror attack in its history on Sept. 11, 2001. From the Pentagon and the World Trade Center to a field outside of Shanksville, Pennsylvania, the attacks left 3,400 people dead. The events of that day also spawned a new era in U.S. foreign policy - one that would lead to thousands more American deaths in the coming decades.
Less than one month after the 9/11 attacks, the War on Terror began when the U.S. and NATO allies started military strikes in Afghanistan. Then, in 2003, the War on Terror escalated further, when the U.S. launched an invasion of Iraq.