CHICAGO — Inside the convention hall, the choreography of American politics stumbled on.

Vice President Hubert Humphrey won the Democratic presidential nomination with 1,761 votes to 601 for Senator Eugene McCarthy. The delegates adopted Mr. Humphrey’s platform, which continued President Lyndon Johnson’s unpopular Vietnam policies , and rejected Mr. McCarthy’s antiwar plank. But their attention was on the radios and television screens reporting chaos outside.

A few miles away, thousands of protesters streamed out of Grant Park into a sea of tear gas and billy clubs. Some were caught in a crush against the facade of a Hilton hotel and fell through the plate glass, cutting themselves on shards. People on upper floors threw crystal ashtrays, one of which struck a passer-by and shattered, embedding glass in his eyes. Blood ran from skulls into gutters. Someone tried to overturn a police van. All the while, the crowd was chanting.

“The whole world is watching. The whole world is watching.”

It was on this night, Aug. 28, that all the anxiety and rage of 1968 exploded. Numerous groups were involved, with different motives and tactics. There were Yippies who said they would get high and have sex outdoors, and black and Latino Chicagoans, including the Puerto Rican leftist group the Young Lords, who wanted to challenge police brutality; McCarthy supporters who sought change within “the system,” and Students for a Democratic Society activists who wanted to shred it.

Some protesters taunted the police, and a small number threw bags of feces at them. But an official report found that the police acted out of proportion to the provocations and largely targeted people who had done nothing to provoke officers. It was, the report concluded, a “police riot” driven partly by Mayor Richard J. Daley, who had earlier given the police license to “shoot to kill” in certain circumstances.