20 years on, America remembers day that changed the world

From left, former President Bill Clinton, former First Lady Hillary Clinton, former President Barack Obama, former First Lady Michelle Obama, President Joe Bien, First Lady Jill Biden, former New York City Mayor Michael Bloomberg, Bloomberg's partner Diana Taylor, Speaker of the House Nancy Pelosi (D-CA) and Senate Minority Leader Charles Schumer (D-NY) stand for the national anthem during the annual 9/11 Commemoration Ceremony at the National 9/11 Memorial and Museum on Saturday, Sept. 11, 2021 in New York. (Photo: AP)

As the world completed 20 years of the worst attack on the United States on September 9, 2001, that killed 2,977 Americans, President Joe Biden urged unity as his country prepares to remember the victims. (AP Photo)

Family members and loved one of victims attend the annual September 11 Commemoration Ceremony at the National 9/11 Memorial and Museum in New York City, U.S., September 11, 2021. (Photo: Chip Somodevilla/Pool via REUTERS)

Flowers are seen on the 9/11 Memorial on the 20th anniversary of the September 11 attacks in Manhattan, New York City, U.S., September 11, 2021. (Photo: REUTERS/Mike Segar/Pool)

Bruce Springsteen performs during the annual September 11 Commemoration Ceremony at the National 9/11 Memorial and Museum September 11, 2021 in New York City, U.S., September 11, 2021. (Photo: Chip Somodevilla/Pool via REUTERS)

Ember Boyle, 6, walks past an American flag ahead of the 9/11 Heroes Run to commemorate the 20th anniversary of the September 11 attacks in Houston, Texas, U.S., September 11, 2021. This photo was taken at 8.46am EDT on September 11, 2021, exactly 20 years after the first plane struck the North Tower of the World Trade Center in New York. (Photo: REUTERS)

The terror attack on US soil has shaped most consequential domestic and foreign policy decisions made by American leadership over the past two decades. (AP Photo)

A woman mourns at the 9/11 Memorial on the 20th anniversary of the September 11 attacks in Manhattan, New York City, U.S., September 11, 2021. (REUTERS Photo)

Family members of victims hold pictures of their loved ones during a ceremony marking the 20th anniversary of the September 11, 2001 attacks at the World Trade Center site in New York City, New York, U.S., September 11, 2021. (Photo: REUTERS)

Names of victims of the 9/11 attacks are seen on a screen in Times Square during the 20th anniversary of the September 11, 2001 attacks in New York City, New York, U.S., September 11, 2021. This photo was taken at 8.46am EDT on September 11, 2021, exactly 20 years after the first plane struck the North Tower of the World Trade Center in New York. (Photo: REUTERS)

Flowers are seen on the 9/11 Memorial on the 20th anniversary of the September 11 attacks in Manhattan, New York City, U.S., September 11, 2021. (Photo: REUTERS)

The milestone anniversary takes place just weeks after the chaotic US withdrawal from Afghanistan and the return to power of the Taliban. (AP Photo)

It also comes after a suicide bomber in Kabul killed 13 US service members as the military concluded its withdrawal from Afghanistan. (AP Photo)

In the immediate aftermath of the 9/11 attacks, there was a spate of hate crimes and rising instances of discrimination against Muslims (AP Photo)

A pedestrian walks past a field of American flags, each representing every victim murdered in the terrorist attacks of Sept. 11, 2001, at the 9/11 Memorial Healing Field, Friday, Sept. 10, 2021, in Tempe, Ariz. (Photo: AP/PTI)

FDNY fireboat sprays water during the 9/11 Boatlift 20th Anniversary Tribute in New York City, New York, U.S., September 10, 2021. (Photo: REUTERS/Jeenah Moon)

A man walks by a 9/11 memorial mural in the Bronx borough of New York City, U.S., September 10, 2021. (Photo: REUTERS/Shannon Stapleton/File)