Thirty years ago this month, President Ronald Reagan went to Germany and issued a striking challenge: “Mr. Gorbachev, tear down this wall.” That wall—the Berlin Wall—came down two years later. Germany became a single nation again, a single united people, ending a half-century of intractable division.

Today, new walls have arisen once again—yet this time, they are right here at home.

The Berlin Wall was imposed on Germany by a powerful outside force: the Soviet Union, determined to force Eastern Germany into communism’s orbit. It was not the Germans themselves who divided their nation into enemy camps on opposite sides of an unbridgeable border. And in the end, it was not the Soviet premier who tore down the Berlin Wall; it was the Soviets, along with the East German government they controlled, that lowered their guns and watched as the German people themselves tore down the wall, and reunited their country.

Unlike in Germany, ours is not a border wall and it has not been forced on us by others; these are walls we Americans have built ourselves, in order to separate ourselves from our own countrymen, our own neighbors, often for the sole reason that these neighbors may not look like us or think like us.

As formidable as it was—a solid and tall mass of concrete and barbed wire, patrolled by heavily armed men with instructions to shoot to kill—the Berlin Wall was, in the end, destructible. The wall that we have erected here in America is built of something invisible, but it may ultimately prove far more powerful and far more dangerous to the future of our country. Its building materials are not concrete and barbed wire but deep-seated distrust, dislike, disdain, and even hatred. Fellow Americans who assess challenges differently, who vote for different parties and candidates, who worship differently, who look different, have come to be seen as alien, “the other.” Yet the more and more we respond by retreating to our own enclaves, living in clusters of people who vote how we vote, think what we think, read what we read, watch the same television shows we watch, shop in the same kinds of stores we shop in, the less we are capable of understanding those who don’t.

Abraham Lincoln was right when he warned that a house divided against itself cannot stand. In our time, the challenges we face are complex and difficult. Technology is drastically revolutionizing the job market: To succeed economically, new generations of Americans are going to need skills and educational credentials far beyond those that have sustained workers for decades and, in some cases, centuries. New health challenges, including opioid addiction and obesity, are wreaking havoc financially, but also in less obvious ways, such as in the ability of our defense forces to find recruits able to meet adequate standards of physical fitness. Partisan media outlets and social networks that promote insularity ensure that people are increasingly out of touch with a variety of opinions, making it more and more difficult to come to shared understandings of what is fact and what is fiction.

Fortunately, none of these problems, nor the myriad of others we face, are insurmountable if we work together with those who may not share our perceptions, to consider varieties of options, and use the collective power of American ingenuity to map out our common future. But that is not where we are today. Our certainty that we are right and that those who disagree are inherently and irredeemably wrong, ill-informed, stupid or evil, has shattered our capacity for common problem-solving. What passes for deliberative democracy today is the brute force of whichever side of our wall has gained a temporary upper hand. Our politicians too often now seem to view this as a goal in and of itself.

So, as was once the case in Germany, it will be up to us, the people, to tear down the wall. History has often shown a great love for irony; within days of this year’s anniversary of Reagan’s speech, Helmut Kohl, the chancellor who presided over the German reunification, passed away. Thanks in great part to his contributions, Germany has become the central power of Europe, a continuing champion of European commonality, and an advocate for peaceful cooperation. Division weakens; unity strengthens.

Gorbachev responded to Reagan’s challenge. We need to respond in the same way: We need to tear down the walls that divide us and put our house back together again. Someone needs to say: “Mr. and Mrs. America, tear down this wall”; it cannot be allowed to stand.