Americans commemorated the 20th anniversary of the September 11 terror attacks with solemn ceremonies to remember the lives lost and to call for a sense of national unity not seen since the aftermath of the deadliest strikes on US soil.
With a tolling bell, a service at Ground Zero in New York on Saturday started exactly two decades after American Airlines Flight 11 crashed into the North Tower of the World Trade Centre. It was the first of four planes Al Qaeda hijacked and used to kill 2,977 people.
“It felt like an evil spectre had descended on our world, but it was also a time when many people acted above and beyond the ordinary,” said Mike Low, whose daughter, Sara Low, was a flight attendant on that first plane.
In the weeks after 9/11, Americans came together in shock and mourning, and countries the world over rallied behind the US in solidarity.
But 20 years and two costly conflicts in Afghanistan and Iraq later, Americans are at war with themselves over any number of issues.
“Following the 9/11 attacks, I was proud to lead an amazing, resilient, united people,” former president George W Bush said in a speech at the memorial in Shanksville, Pennsylvania, where a hijacked plane crashed.
“When it comes to the unity of America, those days seem distant from our own ... So much of our politics has become a naked appeal to anger, fear and resentment. That leaves us worried about our nation and our future together.”
He called on Americans to confront domestic extremists who destroy “national symbols”, a reference to the supporters of former president Donald Trump who desecrated the US Capitol in a deadly rampage on January 6 and tried to overturn the results of last year’s presidential elections.
“The dangers to our country can come not only across borders but from violence that gathers within,” Mr Bush said.
Mr Bush is remembered as rallying the nation in the days after 9/11, including famously giving a rousing speech through a megaphone at Ground Zero three days after the attacks.
But the fiasco of his war in Iraq has been blamed as a root cause for much of the division in the US today.
In a recorded address on Friday, Mr Biden said Americans must strive for common ground.
“In the days that followed September 11, 2001, we saw heroism everywhere, in places expected and unexpected. We also saw something all too rare: a true sense of national unity,” he said.
Mr Biden did not deliver remarks at any of the sites. After Saturday's ceremony in Shanksville, he said: "The core of who we are is not divided" during a visit to a fire station.
Mr Trump meanwhile released a video message slamming Mr Biden’s “inept administration” for its "incompetence” over the Afghanistan withdrawal.
The former president, who had been in New York, did not attend the main memorial service in Manhattan and was to later deliver ringside commentary at a boxing match at a casino in Hollywood, Florida.
Mr Clinton, who was president in the years leading up to 9/11, said: “America will never forget those who lost their lives, those who risked or gave their own lives to save others, and those whose lives were forever changed 20 years ago. We owe it to all of them to come together again with unity, hope, compassion and resolve.”
In addition to the people killed on 9/11, a similar number of first responders who helped clean up the toxic remnants of the attacks are thought to have died of cancer, lung disease and other health conditions stemming from their work in the weeks after the atrocity.
In Britain, Queen Elizabeth II offered her “thoughts and prayers”.
“We also pay tribute to the resilience and determination of the communities who joined together to rebuild,” she said.