The US on Friday began marking 20 years since the 9/11 terror attacks that changed the course of the country's history, reshaped Afghanistan and parts of the Middle East, and ushered in a global war on terror that has cost hundreds of thousands of lives.
Not only does this year's anniversary mark two decades since the attacks, September 11 was also supposed to bring a symbolic end to the US war in Afghanistan, which was triggered when Al Qaeda hijacked four planes and used them as missiles to kill 2,977 people from more than 90 countries in New York, at the Pentagon and in Pennsylvania.
President Joe Biden had set the date as the deadline for the last US troops to leave Kabul and formally end America's longest war.
History, however, did not co-operate, and what was supposed to have been an organised departure from Afghanistan ended in utter chaos last month with the Taliban back in power and Al Qaeda operatives flocking to the country.
In the weeks after the worst attacks on US soil, Americans in 2001 came together in shock and mourning as countries the world over rallied behind the US in solidarity.
But 20 years and two failed conflicts in Afghanistan and Iraq later, Americans are at war with themselves over any number of issues.
And allies who fought in Afghanistan are still reeling from former president Donald Trump's broadsides against Nato and Mr Biden's messy, unilateral withdrawal.
So instead of presiding over a rare moment of national unity, Mr Biden faces a country grappling with the loss of another war and a seemingly unbeatable pandemic that has killed more than 650,000 people in the US.
In a recorded address released on Friday by the White House, Mr Biden appealed to Americans to find common ground.
“No matter how much time has passed, these commemorations bring everything painfully back as if you just got the news a few seconds ago,” Mr Biden said.
“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.”
Mr Biden also lamented the “darker forces” of human nature.
"Fear and anger. Resentment and violence against Muslim Americans, true and faithful followers of a peaceful religion … We learnt that unity is the one thing that must never break”.
Unlike his brash predecessor, Mr Biden has shown many public displays of empathy, something that is likely be on display on Saturday.
But in ruptured America, even his sincerity in grief is being questioned.
Some of the families of the 13 US troops killed in an ISIS attack in Kabul last month said Mr Biden was more concerned about telling the story of his son Beau Biden's death from cancer than he was in hearing about their recently lost loved ones.
Secretary of State Antony Blinken on Friday sought to sound a unifying tone, recalling “one of the darkest days in our history” as he attended a 9/11 ceremony at the State Department.
“Out of it also came these demonstrations of profound humanity, compassion, strength and courage,” he said, and added that 9/11 showed “our remarkable resilience".
“It showed our capacity to defend the pluralism that has long been one of our country’s greatest strengths, including by embracing our Muslim-American brothers and sisters,” Mr Blinken continued.
Mr Biden and his wife, Jill, will commemorate the 9/11 anniversary by visiting all three sites of the attacks.
They will start at Ground Zero in New York, where most of the roughly 3,000 fatalities were tallied. Many died in the initial explosions, others jumped to their deaths to escape the raging infernos as the towers burned, still others vanished as the skyscrapers fell.
They will also take part in ceremonies in Shanksville, Pennsylvania, the site where a hijacked plane crashed; and in Arlington, Virginia, where the Pentagon was struck.
Other ceremonies will be held the length and breadth of the US, including in Guantanamo Bay, where five men accused of assisting the 9/11 hijackers are still awaiting trial.
Troops stationed on the US base carved from a tip of Cuba will go on a 9.11-kilometre remembrance run, and a special service will be held in the chapel.
At the National September 11 Memorial in Lower Manhattan, where the World Trade Centre once stood, families of the victims of 9/11 will read their names as the “Bell of Hope” rings out at 8.46am, marking the moment the first of two planes hit the Twin Towers.