Where the national guard once stood in formation with bayonets fixed, a line of stands for rental bikes now stretches away along South Michigan Avenue.

Where protesters against the Vietnam war once massed, chanting “the whole world is watching”, sun shines on formal flower beds filled with purple hostas and golden lilies.

Across the street, the facade of the Hilton Chicago looms, four towers of brick rising above war-like stone carvings of figures carrying shields and axes. There are few clues, but 50 years ago, this spot was a crucible of violence, which exposed fault lines in a divided and traumatised nation.

A tumultuous season of assassinations, riots and war, 1968 was the year that changed America, in ways that still unfold today. And part of that momentous drama played out on summer nights in Chicago when blood ran in the streets and police orchestrated a riot as anti-war protesters tried to march upon the Democratic national convention calling for an end to the Vietnam war.