In a ceremony at the Pentagon, Afghanistan's president thanked US troops and taxpayers for their sacrifices in nearly 14 years of war.
President Ashraf Ghani also offered assurances that his country would not be a burden on the international community as it continues to struggle against the Taliban and its own internal divisions.
Defence Secretary Ash Carter welcomed Ghani and Afghan Chief Executive Abdullah Abdullah at a ceremony in the Pentagon's centre courtyard.
It was a poignant setting for the start of Ghani's Washington visit.
On September 11, 2001, terrorists hijacked an American Airlines jetliner and flew it into the Pentagon, killing all aboard and 125 people in the building.
The US responded to the attacks on Washington and New York by invading Afghanistan a month later.
