With a full-throated roar of approval and by unanimous vote, the Democratic rank-and-file made history on Wednesday night by handing the party's presidential nomination to a black candidate.

Barack Obama is the first African American to win the nomination from a major political party. But that is not something either Mr Obama or the party leaders wished to dwell on in podium speeches: they do not want the contest to be defined by race.

Thus Mr Obama's mould-breaking achievement went largely unspoken as the former president Bill Clinton, the running mate Joe Biden and other giants of the party declared him fit to be commander-in-chief.

Yet, the Democrats need to win the votes of white working-class Americans, many of whom remain deeply uneasy at the prospect of a black man in the White House.

For most delegates in the convention centre, Mr Obama's nomination was a hugely emotional moment. The contest with Hillary Clinton finally ended as the former first lady swept into the conference centre to ask for an interruption in the roll-call vote so that her opponent could be declared nominee by acclamation.

A page of history had turned, 120 years after Frederick Douglass – the slave turned abolitionist – was awarded one vote at the 1888 Republican convention in Chicago. But the joy was something to be savoured privately, rather than trumpeted from the podium. Outside the hall, John Lewis, a civil rights hero of the 1960s, put the night in perspective: "It makes me think about all the suffering, all the pain, all the hurt, so many people who gave all they had. This is a down payment on the dream of Martin Luther King."

The tone of the evening was set by Mr Biden, who spoke of a childhood struggle with a stammer, and, casting himself as a brawler with a heart of gold, volunteered that his mother, 90-year-old Catherine Eugenia Finnegan Biden, had taught him to punch bullies. "When I got knocked down by guys bigger than me... she sent me back out and said, 'Bloody their nose, so you can walk down the street the next day'," he said.

It is this working-class street cred which will be put to work in the 18 battleground states the Obama campaign has targeted. He will now focus on the vast Appalachian region, where the god-fearing descendants of Scots-Irish immigrants have the highest rates of military enrolment, love their guns and betray a deep unease in the polls at the prospect of having a black president.