In October 2001, President Bush announces that British and U.S. troops have begun airstrikes on al-Qaeda and Taliban bases in Afghanistan in retaliation for the September 11th attacks.
The next month, U.S. troops begin to arrive in Afghanistan and start to search for the leader of the al-Qaeda movement, Osama Bin Laden. By the end of the year, U.S. troops will have overthrown the Taliban and instituted an interim government.
However, the U.S. combat mission in Afghanistan will not formally end until 2014 (with troops remaining after), making it the longest military conflict in U.S. history.