Senator Barack Obama officially announced his bid for president, urging an end to the Iraq war and portraying himself as a fresh face capable of leading a new generation. He is the youngest contender among his fellow Democrats and would be the first black US president if elected. "Let us transform this nation," he told thousands shivering in the cold at the campaign's kickoff Saturday. Obama, 45, is relatively new to national politics, but is already considered one of the top challengers in his party to front-runner Senator Hillary Rodham Clinton in the 2008 election. The first-term US senator from Illinois sought to distinguish himself as a staunch opponent of the Iraq war and a White House hopeful whose lack of political experience is an asset. "I know I haven't spent a lot of time learning the ways of Washington. But I've been there long enough to know that the ways of Washington must change," Obama said to some of the loudest applause of his 20-minute speech. Obama is looking to cap his remarkable, rapid rise to prominence with the biggest political prize of all - the presidency. His elective career began just 10 years ago in the Illinois Legislature. He lost a bid for a US House seat, then won the Senate seat in 2004, a relatively smooth election made easier by Republican stumbles. In his speech, Obama did not mention his roots as the son of a black man from Kenya and a white woman from Kansas, his childhood in Hawaii and Indonesia or the history he would make if elected. That compelling biography has turned him into a political celebrity. Instead, he focused on his life in Illinois over the past two decades, beginning with a job as a community organizer. He said the struggles he saw people face inspired him to get a law degree and run for the Legislature, where he served eight years. Although he is a Democrat, Obama tied his announcement to the legacy of a famous Republican leader, former President Abraham Lincoln, who also began his political career in the Illinois legislature. Lincoln presided over the nation during the Civil War and ordered an end to slavery in 1863 - a declaration that was added to the US Constitution two years later. On Saturday, Obama chose to announce his bid at the building where Lincoln served as a state lawmaker. "We can build a more hopeful America. And that is why, in the shadow of the Old State Capitol, where Lincoln once called on a house divided to stand together, where common hopes and common dreams still live, I stand before you today to announce my candidacy for President of the United States of America," Obama said. His voice rose to a shout as he spoke over the cheers from thousands who braved sub-freezing temperatures. "I know it's a little chilly, but I'm fired up," Obama said as he took the podium with his wife Michelle and daughters Malia, 8, and Sasha, 5, with U2's "City of Blinding Lights" blaring on the speakers. Obama spoke of reshaping the economy for the digital age, investing in education, protecting employee benefits, insuring those who do not have health care, ending poverty, weaning America from foreign oil and fighting terrorism while rebuilding global alliances. But he said the first priority must be to end the war in Iraq. "It's time to admit that no amount of American lives can resolve the political disagreement that lies at the heart of someone else's civil war," he said. He noted that he was against the invasion from the start. After the speech, the family, several dozen members of the media and the new campaign staff boarded a plane - "Obama One," a flight attendant called it - for Iowa, where Democrats are scheduled to have the first chance to vote for the nominee. "I'm in it to win it," Obama declared at a rally in Waterloo, borrowing what has been the signature line of Clinton's early campaign. Earlier, at a town hall meeting in a packed high school gym in Cedar Rapids, Obama spoke for an hour but only had time to take five questions from the audience, covering foreign affairs, defense and education. The audience groaned when he said he had to leave, but he promised to return. "There was a big crowd today," he said. "But let's face it, the novelty's going to wear off." Obama gained national recognition with the publication of two best-selling books, "Dreams From My Father" and "The Audacity of Hope," and by delivering the keynote address at the Democratic National Convention in 2004 - the same year he was elected to the Senate. His optimistic message and personal story immediately sparked talk of his White House potential.