US President Barack Obama says the post-September 11 decade has proven that despite divisions, wars and recession, nothing can shatter the will of America if it remains united.
Obama, who has endured his own rough political patch, said that his nation's response to the world's worst terror attack exactly 10 years ago had shown its ideals were "timeless" and its resilience unquestioned.
The president, wrapping up a day of solemn 10th anniversary commemorations in New York, Pennsylvania and Washington on Sunday, said generations to come would visit memorials to the dead of September 11, 2001 and subsequent wars in Iraq and Afghanistan.
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"They will know that nothing can break the will of a truly United States of America," Obama said, stressing the word united, and cast the fight against terrorism as victory alongside some of his nation's greatest achievements.
"They will remember that we have overcome slavery and Civil War, we have overcome bread lines and fascism, and recession and riots, communism and, yes, terrorism," he said at an tribute event at the John F Kennedy Center for the Performing Arts in Washington.
"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 said that much had changed since al-Qaeda's attacks on New York and Washington, which killed nearly 3000 people and sparked passionate debates and political divides.
"On September 12, 2001, we awoke to a world in which evil was closer at hand, and uncertainty clouded our future," he said.
"In the decade since, much has changed for Americans. We've known war and recession, passionate debates and political divides.
"We can never get back the lives we lost on that day, or the Americans who made the ultimate sacrifice in the wars that followed."
"Yet today, it is worth remembering what has not changed. Our character as a nation has not changed.
"Our belief in America, born of a timeless ideal that men and women should govern themselves, that all people are created equal ... that belief, through test and trials, has only been strengthened."
"These past 10 years have shown that America does not give in to fear."
Obama also paid tribute to his predecessor George W Bush, with whom he had deep political disagreements, but stood side-by-side in unity earlier Sunday at the Ground Zero site of the felled World Trade Center twin towers.
"We have not succumbed to suspicion and mistrust. After 9/11, President Bush, to his great credit, made clear what we reaffirm today: the United States will never wage war against Islam or any religion.
Throughout the September 11 commemorations, there has been a sense that Obama is trying to move his nation on from the fierce recriminations over the war in Iraq - which he opposed - and anger sparked by the war on terror.
The president appeared to be mustering another great national effort, to overcome the worst economic crunch in decades, at the same time as he pushes a $US447 ($A429.56) jobs bill and seeks a second term in office.
His call for patriotism and national purpose will likely be heard often in the run up to the 2012 election, as the president seeks a narrative that will convince voters to send him back to the White House despite tough times.
