Police officers in the US today are increasingly not only armed but heavily armoured.

The author and investigative reporter Radley Balko traces this shift in his book Rise of the Warrior Cop: The Militarization of America's Police Forces.

Balko explains that race riots in the '60s and America's war on drugs in the subsequent decades led police departments to adopt weapons, uniforms and tactics inspired by military special forces. He writes that fears of terrorism after 9/11 accelerated the trend - even in unlikely targets such as rural Idaho.

And he argues that the military appearance of officers today makes it much harder for them to connect with civilians in communities they are policing.

Produced by the BBC's Ashley Semler and Bill McKenna

Picture This is a series of video features published every Thursday on the BBC News website which illustrates interviews with authors about their new books.