When the U.S initiated its invasion of Afghanistan on 7 October 2001 it led to a war that is continuing until now. After the 911 invasion by Bin laden, America declared that Al Qaeda is not a safe base of operations in Afghanistan. On their attack of 2001, they forcefully eradicated the Taliban out of Afghanistan.

After they have met the initial requirements of their plan, America made an association of 40 countries for the formulation of a security mission in Afghanistan called ISAF (International Security Assistance Force). Several country members of this association were already in a dispute with Afghanistan. After this, the war has now acquired the form of Taliban insurgents that fight with the armed forces present in Afghanistan. Most of the soldiers and the expertise of ISAF is American.

https://en.wikipedia.org/wiki/War_in_Afghanistan_(2001%E2%80%93present)