On the night of November 4 2008 young people of every race flooded onto Pennsylvania Avenue in front of the White House to celebrate the election of the US's first black president. They were back on Pennsylvania Avenue and on streets across the nation last week. This time, though, they were angry - shocked by the death of yet another black man in police custody: Freddie Gray.Prior to Gray's death, Eric Garner had been choked to death in July in New York; unarmed teenager Michael Brown had been shot in Ferguson, Missouri, in August; 12-year-old Tamir Rice had been shot in November as he held a toy gun in Cleveland; and Walter Scott was shot several times in the back last month as he ran away from an officer.On Friday, after weeks of riots, police in Baltimore were charged with the murder of Gray while he was in custody.Is it surprising that in just seven years "hope" has been replaced with fury?From a distance it is easy to conclude that any racial progress marked by Barack Obama's election has evaporated. But it is more complicated than that. The election of a black president was not proof that the US had become post-racial. It was, rather, evidence of how far the nation had come. Obama was the product of generations of hard work, integration and reconciliation. Though racism still exists and class still matters, the US has certainly turned a corner from a time when skin colour was the sole determining factor in gaining access to opportunities.But for those without such assets the country still holds peril. There are millions of Americans who are being left behind. The recession of 2008-2009 wiped millions of dollars off property values, especially hurting black Americans. College loans became harder to acquire and students were forced to drop out. Unemployment rocketed. At one point the official unemployment rate for black men was more than 17%.In the midst of these tough economic times, black Americans continue to face bias in the criminal justice system.The Justice Department found that the police in Ferguson routinely violated black people' s rights. Economic hopelessness combined with police brutality is kindling in the tinder box of urban discord.Nonetheless, there are faint signs of progress. More young black people are enrolling in college (though graduation rates are still lagging). Interracial marriage, a key indicator of harmony, is increasing. And large numbers of white protesters have called for action against police brutality. As the younger, more colour-blind generation grows and older Americans leave the political scene, more progress is likely.Police should be receiving "bias awareness" training and body cameras should be standard issue. And if there is a death, independent investigators should be called in to restore trust and accountability. Angry youths should not have to set buildings on fire. But, more importantly, there must be economic parity.The strength of the US has always been a belief that tomorrow might be better than today. It must not let that hope go up in smoke. ..