Sen. Barack Obama became the first African-American elected president with a sweeping victory that for one historic night, and perhaps for much longer, shifted the geographic and demographic maps of American politics.

"If there is anyone out there who still doubts that America is a place where all things are possible; who still wonders if the dream of our founders is alive in our time; who still questions the power of our democracy, tonight is your answer," the victorious Democrat told a vast cheering throng in Chicago's Grant Park.

The child of a Kenyan father and Kansas mother, raised in Hawaii and Indonesia, addressed his acceptance to a world far beyond the celebrating crowd.

"To all those who have wondered if America's beacon still burns as bright," he said, "tonight we proved once more that the true strength of our nation comes not from the might of our arms or the scale of our wealth, but from the enduring power of our ideals: democracy, liberty, opportunity, and unyielding hope."

The first term Illinois senator defeated Sen. John McCain as he buttressed traditional Democratic strongholds with the support of states once safely in the control of Republicans. His Electoral College total was at least 338 to Mr. McCain's 159, and seemed likely to head higher as the final tallies of several closely contested states were resolved.

The Arizona senator and former prisoner of war conceded shortly after 11 p.m., just after the polls closed in West Coast states, assuring the Democrat of his Electoral College majority.

In a somber, gracious concession, Mr. McCain praised Mr. Obama's achievement, on its own terms and as a symbol of progress in a nation with a history shadowed by the issues of race.

"I recognize the special significance [Mr. Obama's victory] has for African Americans, and for the special pride that must be there tonight," Mr. McCain said. "Let there be no reason now ... for any American to fail to cherish their citizenship in this, the greatest nation on earth."

Mr. McCain's hopes of an upset were dashed hours earlier as television networks declared Obama victories in Pennsylvania and Ohio, two big states that the Republican had lavished with his time and scarce campaign resources. They would be followed by more Democratic success in such former GOP bastions as Florida, Virginia, Iowa, and Colorado.

Mr. Obama built his victory on a message of change that energized massive new cohorts of young people and minorities to the Democratic column. At the same time, however, exit polls suggested that his mainstream appeal, oratory and lavishly funded campaign brought the Harvard law school graduate the support of more white voters than any Democratic presidential candidate in a generation.

The McCain campaign was hobbled from the start by a Republican brand battered by an unpopular war, a faltering economy and a president with dismal approval ratings. The economic headwind facing the Republican grew from gale to hurricane force with the international financial crisis that set the stage for the first of the candidates' three debates. Voters told pollsters that they had more faith in Mr. Obama's economic leadership, and Mr. McCain, who briefly led his rival in polling immediately after the Republican convention, was never again able to significantly narrow his lead.

Through a marathon campaign, Mr. Obama, raised by a single mother and his grandparents after being effectively abandoned by his Kenyan father, demonstrated political skills that belied his relative youth and brief political tenure. The victory came after the longest, most expensive, and technologically dynamic presidential race in history. The field got its first entrant nearly two years ago, when Squirrel Hill's own Tom Vilsack, the former governor of Iowa, declared his candidacy. Mr. Vilsack's bid would prove short-lived but the Democratic competition it opened would last until June 4, when Mr. Obama finally emerged as the Democratic nominee after a long, sometimes bitter series of face-offs with Sen. Hillary Rodham Clinton.

Mrs. Clinton's candidacy seemed cloaked with inevitability until the Illinois senator surged to the front of the big Democratic field with his breakthrough victory in the Iowa caucuses in January. Within a week, Mrs. Clinton would rebound with her poll-defying win in New Hampshire. The pair fought to a virtual draw on Feb. 5 in the coast-to-coast Super Tuesday primaries that most analysts, including Mrs. Clinton and her top strategist, had expected to bring an early end to the nomination battle.

Instead, their long slog continued for months. In April, the battle shifted to Pennsylvania, which through the accidents of a tumultuous political calendar, was the focus of seven weeks of campaigning that brought some of the toughest bruises to Mr. Obama's candidacy. It was during that stretch that Mr. Obama's association with his former pastor; Rev. Jeremiah Wright came under white-hot scrutiny. Trying to quench it, the Illinois senator delivered his widely praised speech on race at the Constitution center in Philadelphia.

As though that were not enough to confirm his Pennsylvania challenge, its was in those weeks that Mr. Obama was placed on the defensive by the report of his ruminations on "bitter" rural voters clinging to guns and religion. All of that combined to build the big margin Mrs. Clinton took from the state.

For a time it also reinforced her claim that he could not win big states. Last night's results offered a convincing rebuttal to that thesis as Democrats who had voted for Mrs. Clinton across the country switched their allegiances to Mr. Obama.

Through those battles and on to the fight with Mr. McCain, the Obama campaign rewrote the textbook of contemporary campaigning. In a ground game that proved potent in state after state, the Obama forces wedded that technology to the Bush re-election campaign's model of micro-targeting and labor-intensive, person-to-person mobilization.

In contrasting ways, both Mr. Obama and Mr. McCain started with candidacies rooted in attitudes toward the Iraq War, the dominant issue in the Democratic congressional landslide of 2006. Mr. Obama claimed prescience in his early opposition to the conflict and hammered his rivals, notably Mrs. Clinton, for their votes to authorize the conflict.

At a time when war news had reached a nadir, Mr. McCain steadfastly supported the surge strategy of Gen. David Petraeus and events in Iraq seem to have justified that view. But as the terrain of the race shifted toward economic concerns, a traditional strength of Democrats, Mr. Obama was more adept than his rival at seizing the issue.

Mr. Obama's central themes -- hope, and change -- resonated with an electorate that profoundly disapproved of both the Republican White House and Democratic Congress. Hope was a positive message but its effectiveness rested on a strain of political nihilism. Mrs. Clinton and Mr. McCain successively hammered Mr. Obama on the experience issue, but, to many voters, in an environment in which President Bush and the Democratic Congress had some of the lowest approval ratings in decades, Washington experience was an asset as devalued as Florida real estate.

If Mr. McCain had managed to cobble together a historic upset last night, it would have been only slightly more startling than his achievement in winning the GOP nomination. Like Mrs. Clinton, he had started 2007 as his party's consensus favorite, but his championing of immigration reform alienated crucial conservative elements of the party. That added to the suspicion with which he was viewed by many conservative Christian leaders with whom he had clashed during his first bid for the White House in 2000.

After his campaign all but expired in the summer of 2007, he scaled back and rebuilt if by living off the land in New Hampshire, building an eventual victory town meeting by town meeting. But the Navy veteran continued to fight a two-front war. He locked up his nomination much earlier than Mr. Obama, but wasn't able to capitalize on his head start. Through the summer and right up to his convention, he was still obliged to continue courting his party's conservative base while simultaneously aiming at his Democratic opponent.

That was a major impetus of his surprising choice of Gov. Sarah Palin. The charismatic and socially conservative executive gave the Republican ticket a much-needed injection of enthusiasm. The choice was a success in winning previously estranged conservatives. Hopes that she would lure large numbers of former Clinton supporters proved less realistic, however, and polls showed that she ended up hurting Mr. McCain with many independents and socially liberal voters.

Pennsylvania was an example of that conflicting dynamic. Mrs. Palin was wildly popular and drew big crowds in some of the state's more rural areas. But polls showed that she was a drag on Mr. McCain appeal in other areas, notably the pivotal Philadelphia suburbs which the Democrat by a wide margin. Mr. Obama total of nearly 55 percent of the state's vote was the largest percentage reached by any Democrat since Lyndon Johnson's 1964 landslide against Barry Goldwater. He won 83 percent of Philadelphia's votes, and topped 60 percent in both Montgomery and Delaware counties. The two former GOP stronghholds, where Mr. McCain had campaigned heavily, gave Mr. Obama and even larger share of their votes than Allegheny County, where his tally stood at 57 percent.

Overall, the Democrat's wide margin in the state, seemed to confirm the Democratic drift of the state over the last decade. Pennsylvania has been a key battleground in presidential elections for generations. Yesterday's results reinforce the suggestion that was moving toward a deeper political blue more closely resembling neighbors such as New York and New Jersey.