When radical Islamic terrorists hijacked four commercial airliners on September 11, 2001 and employed them as weapons against innocent Americans, we were instantly shocked and outraged. Those emotions, and others, washed over us in waves in the hours, days and months that followed.

As the dust settled and our understanding grew, we processed the consequences and worked through the grief and anger that accompany any unspeakable tragedy. Americans from all walks of life understood the magnitude of the devastation, destruction and loss, as well as the substantial blow the attack struck against our national pride and sense of security.

But whatever the intentions of the extremists who launched this evil, brutal assault, our response must have surprised them because of how we came together.

Americans transcended differences and divisions to stand as one people, united in sorrow and pain, but also in resolve and purpose. We pledged to move forward with a renewed sense of identity and rekindled compassion for each other.

Yet our own project of self-renewal occurred alongside a new reality.

On September 14, standing on a pile of rubble at Ground Zero, President George W. Bush told rescue workers, “I can hear you! The rest of the world hears you. And the people who knocked these buildings down will hear all of us soon.” In a subsequent address to a Joint Session of Congress he told the American people, “Whether we bring our enemies to justice, or bring justice to our enemies, justice will be done.” Those who provoked this act of war were put on notice.

Shortly thereafter, the United States hunted down the terrorist group Al-Qaeda which orchestrated 9/11, and also removed the Taliban from its rule in Afghanistan as a consequence of having offered a safe haven from which extremists recruited, trained and dispatched adherents committed to inciting global instability and sowing fear.

Through the might of our Armed Forces and confidence in our cause, those objectives were achieved with remarkable speed. The larger mission persisted and eventually Al-Qaeda’s leader and a key architect of modern Islamic terrorism, Osama bin Laden, was also brought to justice.

Now, as our military presence in Afghanistan has ended, the extent to which America’s warriors serve and sacrifice on behalf of the cause of liberty, with humility and care, is more apparent than ever.

Thousands of men and women answered their country’s call and helped wage the Global War on Terror with dignity, skill and honor. This was not a war of conquest. It was, and continues to be, a battle against the enemies of freedom and on behalf of the democratic principles we hold dear. It has been prosecuted by dedicated U.S. service members, for whom we are eternally proud and grateful, with success and stamina.

Two decades after that terrible September morning, we have learned that no amount of retribution, however just and necessary, can fully heal our wounds. That’s why we come together in a Day of Service to pay tribute to all those lost, injured or forever altered by the events of 9/11. We acknowledge and honor them through acts that build up our communities and strengthen the bonds of unity and patriotism that define us.

I encourage every Arkansan and American to find a way to contribute your time and resources toward that end. The benefits serve each of us individually and our country in ways that are hard to measure, but easy to sense.

Now, we reflect on this solemn anniversary by remembering the victims, sharing in the grief of their loved ones, serving causes greater than ourselves in their honor and praying for the heroic Americans working tirelessly to defend our country and way of life. In doing so, we remember that day’s tragedy and triumph in the most personal and meaningful ways possible.

John Boozman is a U.S. Senator from Arkansas. He is a Republican.