Episode 2

Jonny Dymond looks at America's new internal threats, from Islamic extremists and right-wing militias.

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 Two
America is facing a resurgent threat from violent right-wing groups.

The militia movement - a loose collection of groups united by their opposition to the federal government - lost steam 15 years ago after its adherents killed 168 people in Oklahoma City.

But now an emboldened right-wing has given the movement new life.

BBC Washington correspondent Jonny Dymond goes inside the militia renewal.