Former President George W. Bush commemorated the 20th anniversary of the Sept. 11 terrorist attacks on Saturday at the Flight 93 National Memorial in Pennsylvania, recalling a time of American unity and drawing a sharp contrast with the present-day divisiveness of the country's politics.

Bush, accompanied Saturday by former first lady Laura Bush, was in his first year as president when the attacks took place.

"For those too young to recall that clear September day, it is hard to describe the mix of feelings we experienced," Bush said at a ceremony held at the memorial. "There was horror at the scale of destruction, and awe at the bravery and kindness that rose to meet it. There was shock at the audacity of evil, and gratitude for the heroism and decency that opposed it."

He added that "the actions of an enemy revealed the spirit of a people, and we were proud of our wounded nation."

Recalling how the American people responded to 9/11, Bush painted a starkly different picture compared with the embittered politics of the present day.

"In the weeks and months following the 9/11 attacks, I was proud to lead an amazing, resilient, united people," he said, although many Muslim Americans reported facing heightened discrimination in the wake of the attacks. "When it comes to the unity of America, those days seem distant from our own."

He continued: "Malign force seems at work in our common life that turns every disagreement into an argument, and every argument into a clash of cultures. 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."

"I come without explanations or solutions," Bush added. "I can only tell you what I've seen. On America's day of trial and grief, I saw millions of people instinctively grab for a neighbor's hand and rally to the cause of one another. That is the America I know."

Eight months after the Capitol was stormed by supporters of President Donald Trump, Bush warned against domestic extremism, saying that "the dangers to our country can come not only across borders but from violence that gathers within."

"There is little cultural overlap between violent extremists abroad and violent extremists at home," he continued. "But in their disdain for pluralism, in their disregard for human life, in their determination to defile national symbols, they are children of the same foul spirit, and it is our continuing duty to confront them."

In his remarks, Bush paid tribute to the passengers and crew members of Flight 93, which crashed in a field after those on board fought back against the hijackers and diverted them from their intended target. "Many who are now alive owe a vast, unconscious debt to the defiance displayed in the skies above this field," he said.

In the wake of 9/11, Bush led the nation into the war in Afghanistan and, later, the war in Iraq. Speaking less than two weeks after the last American troops left Afghanistan, he acknowledged in his remarks that military actions over the past two decades "have led to debate."

He offered a message for veterans, saying they had been "a force for good in the world" and adding, "Nothing that has followed, nothing, can tarnish your honor or diminish your accomplishments."

This article originally appeared in The New York Times.