How tear gas became the go-to weapon for US police

The riot control agent, often referred to as 'tear gas', has been used in 100 US cities since late May.

While it was banned from war a century ago, it remains a vital police tool around the world.

Some US law enforcement agencies said they used other gases like pepper spray to disperse protesters.

The US Centers for Disease Control and Prevention (CDC) defines tear gas as "chemical compounds that temporarily make people unable to function by causing irritation to the eyes, mouth, throat, lungs, and skin."

Produced by the BBC's Franz Strasser.