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

With those words, Barack Obama officially became the Democratic Party’s nominee for president Thursday night, and launched an historic acceptance speech as the first black presidential nominee of a major party. Undaunted by polls showing him in a close race with GOP rival John McCain, Illinois's junior senator appeared unruffled as he outlined his mission statement as the next president of the United States.

“We meet at 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,” he said.

Expectations were high for Obama’s speech, delivered from Invesco Field in the Mile-High City before a reported crowd of 84,000 people and millions of others watching live around the world, and the Illinois senator, known for his oratory, delivered a rousing call for change.

“These challenges are not all of government’s making," he said. "But the failure to respond is a direct result of a broken politics in Washington and the failed policies of George W. Bush."

Obama told the story of his upbringing, as the son of a Kenyan father and a Kansas-born mother, casting himself as an average American, whose life was shaped by the sacrifices of his single mother and the resilience of his grandparents. He painted a picture of a United States where individuals of all backgrounds can succeed thanks to the support of a caring government.

“It is that promise that has always set this country apart – that through hard work and sacrifice, each of us can pursue our individual dreams but still come together as one American family, to ensure that the next generation can pursue their dreams as well," he said.

As he has in the past, Obama praised McCain's service in the American military, but reiterated that the Republican candidate has voted with Bush 90 percent of the time while in the Senate.

"It's not because John McCain doesn't care. It's because John McCain doesn't get it," Obama said.

Obama sought to counter the criticisms of Republicans. He struck back at the argument that he is risky on national security.

"We are the party of Roosevelt. We are the party of Kennedy. So don't tell me that Democrats won't defend this country," said Obama.

He also addressed concerns about whether he is “ready” to serve as commander-in-chief.

"As commander-in-chief, I will never hesitate to defend this nation, but I will only send our troops into harm's way with a clear mission and a sacred commitment to give them the equipment they need in battle and the care and benefits they deserve when they come home."

Obama touched on several other issues dominating the political landscape, the war in Iraq, rewriting the tax code and energy policy.

"For the sake of our economy, our security, and the future of our planet, I will set a clear goal as President: in ten years, we will finally end our dependence on oil from the Middle East."

He also pledged educational reform, including a raise in teachers' salaries and a community service program that would help pay for college students' tuition.

The final section of his speech dealt with how he felt the common American people were tired of divisive politics and wanted bipartisan solutions to the country's hard-pressing issues.

"I stand before you tonight because all across America something is stirring. What the nay-sayers don’t understand is that this election has never been about me. It’s about you," said Obama.

He finished his speech by marking the 45th anniversary of Martin Luther King, Jr.'s "I Have A Dream" speech, which he said represented Americans' pursuit of a better society.

"America, we cannot turn back. We cannot walk alone. At this moment, in this election, we must pledge once more to march into the future," said Obama.

Once he finished his speech, the loudspeakers played the Garth Brooks song "Only In America," which was used by President George W. Bush during the 2004 campaign. Fireworks then erupted above, while confetti fell onto the tens of thousands of cheering onlookers.

The Republican team immediately released a statement, saying that Obama's speech was "misleading," and that his government record was "meager."

Obama was introduced by senior Illinois Senator Dick Durbin, who also introduced the presidential candidate’s landmark speech in the 2004 Democratic convention, which launched his national political notoriety.

The Democratic faithful also got a chance earlier to listen to another party superstar – former vice president and 2000 presidential nominee Al Gore, who addressed the growing crowd just before 7 p.m., Denver time. Gore delivered a scathing attack on the Bush administration and said that a vote for presumptive Republican presidential nominee John McCain would be a vote for more of the same.

"One of the greatest gifts of our democracy is the opportunity to change course every four years," said Gore. "Will we seize this opportunity?"

Gore also blamed Bush for the country's faltering economy and the war in Iraq, saying that the president has led the nation into one "calamity" after another.

He was preceded by a list of speakers, including Democratic Party Chairman Howard Dean, Virginia Governor Tim Kaine, and a musical performance by Stevie Wonder.

Crews have spent the past few days transforming the open-air football stadium into a speaking hall, with the stage being constructed to resemble the Lincoln Memorial, in an attempt to give it a more intimate feel.

Earlier, the Illinois senator spoke at a luncheon, where he told the crowd he hasn't forgotten where he came from and that it’s because of his supporters that he has the honor of fighting to win back the White House.

Starting at 3 p.m., Democrats began filing in to the stadium, decked in Obama paraphernalia. The mood among those waiting in the long lines to enter the event was more like a rock concert than a political forum.

"This line has the most diverse, positive energy and the most hope that I have felt in years and years," said one Obama backer.

Many musical acts will be performing tonight, including Stevie Wonder, Sheryl Crow, Will. i. Am and Jennifer Hudson.

New York lawmakers said they are looking forward to tonight's address. New York Congressman Charles Rangel even went so far to say, "I cannot think of any other period in my life, with the exception of the Civil Rights movement, that I felt more proud to be an American."

The Reverend Jesse Jackson, who was the first black man to run for the White House and who ran campaigns in 1984 and 1988, had nothing but praise for Obama Thursday.

"We're not just here today for a ball game. We're here for a political development, for emancipation from ancient fears. To remove doubts and to choose hope, and that is a big deal, it seems to be me,” said Jackson. “I do think that on this 54-year journey [since the Supreme Court ruling of Brown vs. Board of Education, which outlawed segregation], Barack is running the last lap of the 54-year relay team."

Jackson found himself in trouble earlier this year, after making off-the-cuff remarks about Obama that were caught on tape during a television interview.

Last night, it was Obama's running mate Joe Biden who had his time in the spotlight. Biden accepted the party's nomination as vice president and wasted no time going after the opposition. Despite calling presumptive Republican nominee John McCain a friend, Biden said the nation requires more than just a good soldier in the White House.

Biden was joined on stage after his speech by Barack Obama. Just hours after becoming the Democratic nominee, Obama talked again about his campaign's philosophy of inclusion.

Earlier in the night, former President Bill Clinton delivered a strong speech in support of Obama. Clinton tried to heal the wounds of the bitter primary fight, urging those who supported his wife to vote for Obama.

He likened Obama's quest for the presidency to his own bid in 1992, when Republicans said he was too young and inexperienced to be president.

"Barack Obama is ready to lead America and restore American leadership in the world," said the former president. "Barack Obama is ready to honor the oath to preserve, protect, and defend the Constitution of the United States. Barack Obama is ready to be president of the Unites States."

The former president's speech came a few hours after his wife, Hillary Clinton, helped Obama become the party's official choice.

Surrounded by her colleagues from New York, Clinton asked the delegates to call off the roll-call vote – which was designed to honor her own historic campaign.

Mrs. Clinton said she made that request "in the spirit of unity" and "with the goal of victory."

Republican rival John McCain is congratulating Obama in an ad that will run only tonight.

"Senator Obama, this is truly a good day for America. Too often the achievements of our opponents go unnoticed. So I wanted to stop and say, congratulations,” says McCain in the ad. “How perfect that your nomination would come on this historic day. Tomorrow, we'll be back at it. But tonight, senator, job well done."

Meanwhile, McCain remains silent on his pick for a running mate, but will release the name Friday, when they will appear at a rally Friday in Ohio.

Sources say the Arizona senator made his decision Wednesday.

Two GOP campaign officials told the Associated Press that either Minnesota governor Tim Pawlenty or former presidential candidate and former Massachusetts Governor Mitt Romney is the pick.

The potential vice presidential picks are keeping a low profile.

Minnesota Governor Tim Pawlenty canceled all his media interviews and said he will be at the state fair in Minnesota on Friday.

Romney left his home in Massachusetts Thursday for an unspecified location in California.