On Saturday, the 20th anniversary of the September 11th terrorist attacks will be marked.
For the families of the victims, it will be a painful reminder of the loved ones they have lost.
But this year's anniversary will also mark the start of a new era in American foreign policy, following the end of the US war in Afghanistan.
At the September 11th memorial in New York City, water cascades into two pools that sit in the footprints of the Twin Towers.
The enormous fountains are lined by plaques bearing the names of those who died.
It is a calm, reflective place - a far cry from the chaos that gripped this exact spot two decades ago.
On 11 September 2001, almost 3,000 people were killed when hijackers crashed planes into the World Trade Center, the Pentagon and a field in rural Pennsylvania.
20 years on, it is a day that the world, and in particular New Yorkers, will never forget.
I spoke to Kevin Daly at the 9/11 Memorial and he described the attacks as "devastating".
"I lost a fair amount of friends, I knew a lot of people who lived and worked here. It was a dreadful day. It has been 20 years and time passes but you just hope something like that never happens again," he said.
Donna Tucker also lost friends in the attacks.
"I am a Port Authority retiree, so I lost a lot of co-workers. I can't even tell you a number because I knew so many people who died," she said.
Frank Scozzafava said he doesn't need an anniversary to be reminded of the horrors of the World Trade Centre attack.
"It was the worst day in American history. What's the difference if it was 20 years, 21 years, 18 years? It is every day, you come down here and you are reminded every single day," he said.
Irish American New York firefighter Sean Tallon was among those killed.
His sister Rosaleen recalled how excited he was leaving for work on the morning of 11 September because his probationary period as a trainee firefighter was coming to an end.
"He just seemed really happy. He was beaming, so I like to think he was already on his way to heaven," she said.
Sean was among the first fighters to arrive at the scene.
"His firehouse was the firehouse of the World Trade Centre. I picture him there and I picture how nervous he must have been because he was a new fireman. This would have been one of his first fires," Rosaleen said.
The attacks led to the US invasion of Afghanistan and the toppling of the Taliban. Last month, America's longest war finally ended but not without a chaotic withdrawal and further loss of life.
Retired Lieutenant Colonel Daniel L Davis served two deployments in Afghanistan with the US military and believes the war should have ended years ago.
"I wrote as early as 2009 that this was not working and that we should withdraw our combat forces. In 2010, I warned that if we didn't make major changes, we would lose the war. The very things I pointed out 11 years are precisely the things that led to this defeat," he said.
Daniel does not believe the withdrawal has made the world less safe or heightened the risk of future terror attacks now that the Taliban is back in power.
"I am very confident that we are every bit as safe now as we were five years ago, ten years ago and will be tomorrow. Our security from terrorist threats has never depended on troops on the ground in Afghanistan, Iraq, Syria, Yemen or Somalia. If anything, having Americans on the ground in these places keeps the threat alive," he said.
The September 11th attacks have had a massive impact on American foreign policy for the last two decades.
Tom Wright is a senior fellow at the Brookings Institution in Washington and believes this year's anniversary is different.
"Apart from the fact that it is the 20th anniversary, President Biden has basically indicated that he wants to close the book on the post 9/11 era. That is not to say that the US won't be fighting terrorist networks or trying to thwart attacks with allies but it won't be the single most important issue in US foreign policy and national security policy," he said.
"It is partly about China, party about climate, partly about pandemics and a wide array of other foreign policy issues that to some degree have been neglected over the last twenty years because of this singular focus," Tom added.
But while American foreign policy may be moving on from September 11th, for people like Rosaleen Tallon who lost loved ones on that day, the anniversaries are as painful as ever.
"This year is especially hard because I am battling breast cancer. We are hoping that we can still get to the memorial and that there will be a way for me to go to mass. Our faith has been the glue that kept us going for the last 20 years. We just keep praying, knowing that we will meet Sean again please God," she said.
