The concert, which was organized by the National Cathedral was relocated to the Kennedy Center due to an accident at the cathedral site.
"Nothing can break the will of a truly United States of America," Obama told the crowd, closing a frenetic day on which he attended events in the three places rocked by the terror strikes: Ground Zero in New York City; Shanksville, Pennsylvania; and the Pentagon outside Washington.
The crowd warmly welcomed Obama's praise for an America in which "we have overcome slavery and Civil War; bread lines and fascism; recession and riots; Communism and, yes, terrorism.
"They will be reminded that we are not perfect, but our democracy is durable, and that democracy -- reflecting, as it does, the imperfections of man -- also gives us the opportunity to perfect our union," Obama added, as a montage of images of the worst attacks on US soil were shown on large television screens, and the US president said the concert would "honor those who died."
The music was diverse like America: from a Marines chamber orchestra to the National Cathedral choir; to performances by country, rhythm and blues, and opera-style performers.
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