The US invaded Afghanistan 16 years ago. The Taliban were swiftly driven out, but after decades of war, the country’s roads, schools, and cities were destroyed, so the US and partnering countries poured billions of dollars into rebuilding Afghanistan. One of the highest priorities, most touted by the US, was the project to rebuild the Ring Road. It would run in a 3,200-kilometer loop around Afghanistan, connecting its four largest cities. The US hoped it would connect isolated communities across the country, bring commerce, increase security, and extend the new Afghan government’s influence.

But after 16 years, $3 billion has been spent on the Ring Road, and it remains unfinished. In fact, it’s rapidly deteriorating. The Taliban have swept back through Afghanistan and now claim almost half the country.

Watch the video above to understand how the US mission to rebuild Afghanistan failed. You can find this video and all of Vox’s videos on YouTube. Subscribe for the latest.