In response to the September 11 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.

Which country was invaded by the U.S. in October 2001?