How long has the US been at war in Afghanistan? Why has this war lasted so long?

The US is still at war with Afganistan . There are many reasons for this. But they include a combination of fierce Taliban resistance, the limitations of Afghan forces and governance, and other countries' reluctance to keep their troops for longer in Afghanistan.

The US has now been at war in  Afghanistan for 13 years making it the longest war in US history.

Explanation:

The reason for the longevity of the war is the never ending persistance of the taliban. Another reason is the difficulty american troops have navigating unknown terrain and trying not to cause any harm to the native people of Afghanistan.