Democrat Barack Obama wrote his name indelibly into the pages of American history on Wednesday, engineering a social and political upheaval to become the country's first black president-elect in a runaway victory over Republican John McCain.

The 72-year-old Arizona senator quickly called his opponent to concede defeat and congratulate his rival in the longest and most costly presidential campaign in American history.

McCain spoke graciously at an outdoor rally in Arizona, commending Obama on his victory and emphasizing that he understood its special importance to African-Americans.

"The American people have spoken, and spoken clearly," McCain told disappointed supporters in Arizona, many who booed and growled as he called for the nation to unify behind the victor and his running mate, Joe Biden.

The 47-year-old Illinois senator, son of a white mother from Kansas and an African father from Kenya, mined a deep vein of national discontent, promising Americans hope and change throughout a nearly flawless 21-month campaign for the White House.