Illinois Sen. Barack Obama accepted his party's nomination for president Thursday night at the conclusion of the Democratic National Convention in Denver.

"With profound gratitude and great humility, I accept your nomination for presidency of the United States."

Obama cast his presidential nomination as proof that no dreams are too high, savoring a historic moment for himself and the nation before setting out on a difficult struggle to break another barrier for a black American.

Obama's success in obtaining the Democratic nomination was indeed a remarkable achievement, reached despite the misgivings of some Americans uncomfortable with electing the son of an African immigrant, not "the typical pedigree" as he put it.

He used his acceptance speech in part to allay those concerns, to show Americans that he is one of them, not born of wealth or privilege, his gains made of hard work and sacrifice. "This moment, this election, is our chance to keep, in the 21st Century, the American promise alive," Obama said.

He put himself in the shadow of great leaders like John Kennedy, Franklin Roosevelt and Martin Luther King, Jr., as well as his humble parents. This night came on the 45th anniversary of one of the greatest speeches in American history, King's "I Have a Dream" address.

Obama's speech was the culminating moment of the Democrats' four-day convention, the launching point for a difficult fall campaign against McCain.

When it was over, Obama stood before the cheering crowd, the waving flags, surrounded by family and friends and basked in the moment. It followed an exhausting coast-to-coast primary race with an immediate challenge ahead. Come Friday morning, Obama was embarking on a bus tour of Midwestern battlegrounds where he's running close with McCain.

Fireworks lit the night sky as Obama, his speech concluded, accepted the cheers of supporters. His wife Michelle and their daughters Malia and Sasha joined him as the country music anthem "Only in America" filled the stadium. Vice presidential running mate Joseph Biden and his wife Jill joined them onstage.

Obama delivered his 44-minute nomination acceptance speech before an enthusiastic crowd of 84,000, unprecedented for a political convention that literally shook the stadium at Invesco Field at Mile High with their stomping feet, every participant equipped by organizers with an American flag. More important was the audience of millions of Americans watching on television, a tougher crowd, as Obama spoke before a backdrop of columns reminiscent of the White House portico.

Looking for validation, Obama gave unknown Americans from battleground states prime-time speaking roles to explain their struggles and how the candidate could help them. And Obama himself highlighted the stories of working class Americans, the kinds of voters who have expressed wariness of his candidacy, the woman about to retire in Ohio worried about health care costs, the Indiana worker who lost his job to competition from China, the veterans living on the streets or in poverty, the military families in the midst of repeat tours of duty.

He wanted them to know he was one of them. He said he sees his World War II veteran grandfather in the faces of veterans returning from Iraq and Afghanistan, recognizes his mother in the overworked student yearning to give her children a better life and hears his grandmother in the voice of the businesswoman facing workplace discrimination.

"I get it," Obama said. "I realize that I am not the likeliest candidate for this office. I don't fit the typical pedigree and I haven't spent my career in the halls of Washington. But I stand before you tonight because all across America something is stirring. What the naysayers don't understand is that this election has never been about me. It's been about you."

For those voters with another concern, that a first-term senator who just turned 47 isn't experienced enough to lead the country, Obama had an answer, too, in a list of policy proposals that he argued would improve their lives. He promised tax cuts that would benefit workers, an end to dependence on Middle East oil, more funding for education, health care for every American and an end to the war in Iraq.

"America, now is not the time for small plans," Obama said. And he tried to raise concerns about his rival, Republican John McCain, by saying he's too much like the unpopular President Bush.

"John McCain has voted with George Bush 90 percent of the time," Obama said. "I don't know about you, but I'm not ready to take a 10 percent chance on change."

Obama pledged to jettison Bush's economic policy and replace it with his own designed to help hard-pressed families. "I will cut taxes for 95 percent of all working families. Because in an economy like this, the last thing we should do is raise taxes on the middle class."

The speech didn't mention it, but Obama has called for raising taxes on upper-income Americans to help pay for expanded health care and other domestic programs. He did not say precisely what he meant by breaking the country's dependence on Mideast oil, only that Washington has been talking about doing it for 30 years "and John McCain has been there for 26 of them."

With the nomination in hand, Obama could afford to pause, if only for a moment, to reflect on the path that took him from untested rising star at the Democratic convention just four years ago to the party's standard-bearer this time and a symbol of hope to millions of Americans yearning for change.

Obama himself took note of the transformation. "Four years ago, I stood before you and told you my story of the brief union between a young man from Kenya and a young woman from Kansas who weren't well-off or well-known, but shared a belief that in America their son could achieve whatever he put his mind to."

Then he launched himself into the task at hand, persuading voters that he is the leader for "one of those defining moments, a moment when our nation is at war, our economy is in turmoil and the American promise has been threatened once more."

Obama didn't flinch from offering himself as ready not only for the title of president, but also of "commander in chief." "If John McCain wants to have a debate about who has the temperament and judgment to serve as the next commander in chief, that's a debate I'm ready to have."