"We have come to the end of a long journey. The American people have spoken, and they have spoken clearly," McCain said last night.
He credited Obama with "inspiring the hopes" of millions of Americans.
"This is an historic election, and I recognize the special significance it has for African-Americans and for the special pride that must be theirs tonight," McCain said in Phoenix.
Obama built a national advantage as the financial crisis unfolded in late September, with voters saying they perceived Obama as more responsive than his rival to the urgency of the housing collapse and credit crunch.
Marylanders voted for Obama by a margin of more than 2-to-1, delivering him, as expected, one of his strongest showings of the day.
Half the voters in Maryland said they were "excited" by the prospect of an Obama administration, compared with just one in 10 who expressed the same sentiment about McCain, according to the exit poll conducted by Edison Media Research.
Sen. Benjamin L. Cardin, a Maryland Democrat, called Obama a "transformational leader." Gov. Martin O'Malley said: "It's nice to have our country back. It's been a really miserable eight years."
A Democratic administration in Washington, the governor said, could help the state on health care and other issues.
Obama and McCain were the last survivors of the longest and most expensive campaign presidential campaign ever waged, with $1.5 billion raised by candidates through the middle of October, according to the Federal Election Commission.
Obama built an organization that has changed the face of electoral politics. Reversing a promise, he rejected public campaign financing and raised $639 million, nearly half in contributions of $200 or less, from 3.2 million donors. That meant that roughly one in 20 people who voted for Obama had given to his campaign.
By agreeing to the public system, McCain was limited to $85 million for the general election, and raised $335 million in all.
Embracing new technologies, the Obama campaign built an unprecedented database of volunteers, connected through the Internet and spurred to action through e-mail and social networks.
In Maryland, clusters of Obama volunteers gathered every weekend at meeting points and headed to Virginia and Pennsylvania, competitive states where their enthusiasm could have more impact.
The excitement for his campaign, particularly among African-Americans, led to long lines at polling places in Maryland and other states with large minority populations.
