Dallas. The name was already a byword for political violence before Thursday’s massacre – the place where Lee Harvey Oswald shot John F Kennedy in 1963 and shattered America’s post-war innocence.

Now, five local policemen lie dead, killed while serving their community. Others fight for their lives.

The bloodshed at what was supposed to be a peaceful rally on Thursday night was plainly a hate crime. But how do we define this hate? Was this an act of terrorism, an assault inspired by racial tensions, or both?

Whatever the motives behind this madness, race is back at the top of the agenda in America. The country’s first black president may be in Poland, at a Nato summit designed to stamp on Russian aggression, but he could soon need to return to put out the flames in his own country. That is not the progress he promised.

For black Americans, innocence was lost long ago. Violence has been the norm for centuries. A study conducted last year found that black Americans are more than twice as likely to be unarmed than whites when killed in incidents involving the police. The protest at the centre of Thursday’s horror was a response to the “death-by-cop” this week of two more black men.