President George W. Bush first used the term "war on terrorism" on September 16, 2001 on the South Lawn at the White House. He used the term "war on terror" on September 20, 2001 in formal remarks to Congress.

On October 7, 2001, the U.S. and United Kingdom launched "Operation Enduring Freedom" in Afghanistan, marking the beginning of the War in Afghanistan. As of August 2017, the U.S. has about 11,000 troops in Afghanistan.

The U.S. and coalition forces invaded Iraq on March 20, 2003 under the code name "Operation Iraqi Freedom." U.S. troops withdrew from Iraq by December 2011, ending the Iraq War.

The United States is still actively engaged in a global war on terror, particularly in Afghanistan and against the Islamic State (or ISIS).

Graphic via Business Insider

Infographic via Time