The US' war in Afghanistan has entered its ninth year, making it the longest in US history.

Originally, the mission centred on pursuing and defeating al-Qaeda in the aftermath of the 9/11 attacks.

Many critics say attention to that mission slipped during the Bush administration as the president focused on Iraq.

However, what was never clearly defined to the world or the American public is what a successful Afghan mission would look like and how it would be accomplished.

Now, as the US triples its ground forces, we ask Richard Holbrooke, the special representative for Afghanistan and Pakistan: What does the US hope to achieve and how long will it stay?

This episode of Riz Khan aired from Tuesday, September 21, 2010.