The events of Sept. 11, 2001, changed the lives of Americans forever.
In a recent poll by USA TODAY/Suffolk University, 60% of 1,000 people surveyed agreed.
Eighty-five percent polled said the terror attacks had a big impact on their generation, while nearly two-thirds said it had a big impact on their own lives.
From technological advances to changes in national security, exactly what has changed in the 20 years since America came under attack?
Just 11 days after terrorists crashed planes into the World Trade Center towers in New York City, the Pentagon in Washington, D.C., and a field in Shanksville, Pennsylvania, the Department of Homeland Security was created.
Former Pennsylvania Gov. Tom Ridge was appointed as the first director of the department, which was tasked with overseeing and coordinating a national approach to protect the U.S. against terrorism and future attacks.
The Department of Homeland Security now consists of more than 240,000 employees who are responsible for aviation and border security, cybersecurity and other preparedness measures.
Technology has seen its fair share of changes in the last 20 years.
"Government agencies and private companies have beefed up their disaster preparedness and telecommunications providers have strengthened their digital infrastructure," wrote Darrell West, senior fellow at Brookings' Center for Technology Innovation and its director, Dr. Nicol Turner Lee, in an online article entitled "How technology and the world have changed since 9/11."
Since 9/11, "the United States realized the importance of mobile communications during terrorist attacks and natural disasters," the article says.
"Steps have been taken to safeguard vital networks, which is a huge advancement since 9/11 when thousands of people in New York, and in the area of the Pentagon bombing had to run and walk for miles to what appeared to be a safe space for shelter," the experts continued. "Back then, we didn’t even have voice-activated internet-enabled navigational tools that could advise pedestrians and drivers of road closures, or other potential road or walking hazards."
In October 2001, the U.S. Patriot Act was enacted, which gave the government more authority to investigate potential threats through surveillance of phone calls, emails and text messages.
"With the advent of smartphones and the prevalence of electronic communications, public authorities also developed new tools for monitoring particular individuals and tracking their physical whereabouts via geolocation data," West and Lee's article says. "Twenty years after the attack, the country continues to debate where to draw the line between promoting personal privacy and protecting national security."
It's easy to wonder if the world's technological advancements had happened sooner, whether 9/11 could have been prevented.
Remember the days when you could arrive at the airport 30 minutes before your flight and head straight to your gate?
In 2001, that's what travel looked like. Families could come through security to send off loved ones and, even if you didn't have photo ID in your carry-on bag, blades and liquids were allowed.
But on Sept. 11, 2001, 19 hijackers were able to board four different domestic flights and carry out the attacks that killed thousands. That's when air travel changed forever.
The attacks changed the nation "automatically, immediately, into one obsessed, in big ways and small, with protecting its security," historian James Mann wrote in 2018. "The way that 325 million Americans go through airports today started on Sept. 12 and has never gone back to what it was on Sept. 10."
Tougher security measures were introduced when air travel resumed on Sept. 14, 2001, but the comprehensive Aviation and Transportation Security Act was passed into law by Nov. 19, 2001.
Here are some of the changes to air travel in the U.S. since 2001:
• All passengers over 18 need valid government-issued identification to fly, even on domestic flights. Those identifications are checked against passengers' boarding passes.
• The No Fly List was born — a branch of the Terrorist Screening Database noting people banned from boarding commercial aircraft into, out of and inside the U.S.
• The Transportation Security Administration (TSA) was introduced in November 2001 and took over all airport security functions.
• Potential weapons like blades, scissors and knitting needles are no longer allowed on board, and airport employees are now better trained to detect weapons or explosives. In 2006, a foiled plot to detonate liquid explosives on multiple transatlantic flights led to the restrictions of liquids, gels and aerosols in carry-on luggage that still exist today.
• Also in 2006, the TSA started requiring passengers to remove their shoes to screen for explosives.
• In March 2010, full-body scanners began to be installed in U.S. airports in addition to metal detectors.
• In July 2017, TSA began requiring all personal electronics larger than a cellphone to be placed in bins for X-ray screening.
In addition, bulletproof and locked cockpits became standard on commercial passenger aircraft within two years of the 9/11 attacks. The Arming Pilots Against Terrorism Act became law in 2002 and, in 2003, weapon-carrying pilots started boarding U.S. commercial flights.
Michelle Wright, a reporter for sister station WTAE in Pittsburgh, Pennsylvania, remembers dropping off her son for his first day of preschool on Sept. 11, 2001, and holding her 1-year-old baby at home as she watched the first plane hit one of the towers of the World Trade Center.
"I was stunned," she said.
By the time she got to work, two other planes had crashed — another at the second tower of the World Trade Center and a third at the Pentagon — and there were reports of a plane down in Shanksville, less than two hours away. She and reporter Mike Clark rushed there, but had limited information about whether all of the crashes were related.
Wright and Clark were some of the first media on the scene.
"We just started going live," she said. "That shift turned into a nonstop week of being there. We immediately knew the significance."
Wright said the WTAE crew stayed in hotels and had to go to local stores for clothes and toiletries. They worked from about 3 a.m. until 8 p.m. each day in a world that didn't have social media and in an area of very poor cell reception.
"The public was glued to the television," she said. "People were just really eager to figure out what was going on."
Wright said in her career as a journalist, she can't remember a time when the information she was reporting was more important. Many broadcast stations dropped commercials during that time to make sure that reporters could relay the latest details.
"People were just waiting to find out what was happening to our country," she said.
Wright acknowledged that many relied on cable networks, morning newspapers and radio for breaking news in 2001. Today, however, many people would turn to their phones for instant information.
And, while social media often houses opinion, speculation and misinformation, it allows the public more access to reporters in today's world.
If an attack of that size took place today, the public may not have found out when a plane hit the north tower of the World Trade Center, but from a tweet from a passenger saying their plane had been hijacked.
Instead of circulating stories about passengers rushing the cockpit of United Airlines Flight 93 to confront hijackers before the plane, video or photos of the actual encounter may have been posted online in today's world.
Camera footage would also show a clearer picture of the horror of the attacks, the victims and the aftermath.
In 2001, television news crews made editorial decisions not to show footage of people leaping or falling to their deaths, while networks eventually stopped showing reruns of planes striking the towers to prevent children from thinking the attacks were happening again.
Social media doesn't have that type of editorial censorship.
"As panic-inducing as it was and as tragic an experience it was historically in this country, had the current technology been around in 2001, I think you would have had something far more heart-wrenching," said David Friend, author of "Watching the World Changes: The Stories Behind the Images of 9/11."
Wright said her experience covering the story of United Flight 93 taught her that passing along information to viewers allows them to make decisions, but also make a difference.
"Knowledge is power," she said. "And it's empowering."
She'll also never forget the moment the loved ones of the passengers and crew of Flight 93 were bussed to the crash site for the first time. Without cell phones capturing footage or even cameras rolling, members of the community lined roughly 30 miles of roadway from where the families were housed to the strip mine where the crash occurred to offer their condolences and support.
"Everyone at the site just froze," she said. "It was a powerful moment. All of our lives were changed."
The Associated Press and CNN contributed to this report.