America devotes vast resources to countering external threats, and the past decade's wars in Afghanistan and Iraq have focused attention abroad.

However, there are signs that the next big challenge to US security could come from within the country.

Episode One
Until now nearly all large scale terror plots directed at the US have been orchestrated by overseas groups.

But now there are signs that some native born American Muslims are becoming radicalised, and turning their sights on their own country.

BBC Washington Correspondent Jonny Dymond, examines this new trend and finds out more about this latest threat to American security and multicultural values. Show less