Two decades ago, violent extremists attacked the United States of America.

Twenty years have passed since Sept. 11, 2001. That fateful day, a pair of planes brought down the Twin Towers of the World Trade Center in New York. More than 2,000 American lives were lost there.

How did we respond? We came together.

Two more planes were used as weapons against our nation that same day. One struck the Pentagon, killing 125, and the other — likely headed for the U.S. Capitol — crashed in a field at Shanksville, Pennsylvania after its 40 passengers rallied and rose up against the four hijackers who had taken control.

Like the rest of the nation did in the days that followed, those passengers on United Airlines Flight 93 came together in defense of our country.

Among the people who died that day in addition to civilians were more than 300 firefighters and more than 70 law enforcement officers.

We must never forget the sacrifices all of those brave individuals made. And we must not forget that we are the United States of America.

Looking at our country today, the word united might not come to mind. Yet just 20 years ago, when we faced one of the most horrifying days in American history, unity is what helped so many of us make it through.

Rather than succumb to grief and fear, we proudly waved the American flag — knowing that the freedom it signified was what our enemies feared most. Men and women who were called to serve in the military in the days that followed bravely answered, and the rest of us turned out in droves to see them off and to support the families they left behind until they could safely return home again.

Rather than letting our differences divide us, we remembered that our diversity and our devotion to liberty had only made us stronger.

So as we look back today on Sept. 11, 2001, let’s recall what we learned then — that we are all Americans and that, together, we can overcome anything.