The United States and NATO invaded Afghanistan 20 years ago in response to the terrorist attacks of 9/11 by al-Qaida, harbored by the Taliban.
Now that the Taliban are back in power, there are already worries that Afghanistan will again become a breeding ground for Islamic radicalism and terrorism, aided by new technologies and social media.
These are early days and experts disagree on how the Taliban may choose to govern and on how big a threat they might become, or how quickly.