What does the slogan 'Black Lives Matter'

The phrase "Black Lives Matter" was already hotly debated - and that was before it was reportedly used by the suspect who is thought to have killed five police officers during a sniper attack in Dallas.

Over the past three years, a powerful hashtag and movement has grown up to protest against police killings of black people in America.

More than 1000 people were killed in police operations in the US in 2015, nearly a third of them black - despite the fact that black people are 13% of the population. 

A protest movement has grown up against that but is is a complex, amorphous group: both a formal organisation and, at the same time, a vast informal collection of ordinary people who tweet the slogan Black Lives Matter.


The hashtag surges with each new case of a police killing of a black person that is seen as unjust, usually after a video emerges. 

This week it surged twice - with the fatal shootings of Philando Castile in Minnesota and Alton Sterling in Louisiana.

Each time it surges, mostly peaceful protesters come out in US cities to declare that "Black Lives Matter". It's such a powerful rallying cry that some have controversially likened it to a reborn US civil rights movement. 

That's what was happening in Dallas on Thursday night - a peaceful Black Lives Matter protest - until suddenly, it was anything but. 

The sniper fire at that protest eventually led to the murder of five Dallas police officers and the wounding of seven more. Two civilians at the protest were also wounded.

nd now, the phrase Black Lives Matter is suddenly on everyone's lips - and not in the way its supporters would like.