Many readers may not know this, but today is a significant day in Civil War history. On April 26, 1865—17 days after Robert E. Lee’s surrender at Appomattox—Confederate Gen. Joseph E. Johnston surrendered the Army of Tennessee at Greensboro, North Carolina. The last major Confederate combatant command stacked its arms.

I think of this day not merely because of its national historical significance but also because of its personal family importance. My ancestors fought for the Army of Tennessee. In fact, my ancestors marched across the very ground where my house sits and fought for their lives in the very town—Franklin, Tennessee—where I now live. Other ancestors fought for the Army of Mississippi. I’ve walked their battlefields at Shiloh and Vicksburg.

And I must confess, the older I get, the more I’m haunted by their legacy.

I don’t mean that in a guilty way, as if I’m somehow responsible for the actions of men who took up arms for an unjust cause more than a century before I was born. Instead, I mean that I’ve often asked myself, “What would I have done?”

Slavery was a monstrous evil. Yet generations of Americans grew up in communities that accepted it, defended it, and even celebrated it. How many abolitionist arguments did a child of the antebellum South ever hear? If they heard abolitionist arguments, did they hear them portrayed fairly, accurately, and sympathetically?

Putting aside the power of argument, did the witness of their own eyes and ears—the brutality that was plainly before them—provide them with sufficient cause to say, “No. I shall not defend such evil”?

Let’s put the question differently. Looking realistically at human nature, at the tidal forces of tribe and history, and the immense fallibility of our own hearts, how would each of us answer this question: “If everyone around me is wrong, would I have the wisdom and courage to know and do what’s right?”

My Sunday newsletter last week—arguing that Trump-supporting white Evangelicals had abandoned the character test for candidates and were now even abandoning even the expectation of competence—sparked an immense amount of discussion, debate, and even more than a little bit of anger. Some of that anger centered around my repeated use of the term “white Evangelical.” Why racialize religious Trump support?

I used the term to be precise and fair. If we want to talk about religious Trump support, we are talking about a distinct American community—not all Evangelicals, but white Evangelicals. I linked to polling showing that most other Evangelicals oppose Trump, even if they have the same theological beliefs as their white brothers and sisters. The disparity is so great, that it raises the question—when speaking of white Evangelical support for Trump, is the truly operative word “white” or “Evangelical”?

I’ve been thinking a great deal about the incredibly powerful pull of tribe over truth. I just last week finished the final edits of my new book, called Divided We Fall. The theme of the book is simple—our national divisions are growing so great that we cannot take for granted our continued national unity. I spend an extended amount of time talking about a sociological reality that is ripping our nation to shreds—the law of group polarization.

The concept comes from a Cass Sunstein academic paper, published all the way back in 1999. Surveying the relevant social science, Sunstein said, “[I]n a striking empirical regularity, deliberation tends to move groups, and the individuals who compose them, toward a more extreme point in the direction indicated by their own predeliberation judgments.”

In plain English, this means that when like-minded people gather, their views get more extreme. Our arguments reinforce one another to such an extent that the entire group will sometimes become more extreme than the most extreme person at the start of the deliberation. Think of it like this—when gun rights advocates (or gun control activists) gather, do they tend to leave the meeting doubting their positions or redoubled in their commitment to advocacy? How many people leave a good Bible study loving Jesus less?

It’s a nonpartisan, human phenomenon, and what’s so seductive about it is the fact that we can’t perceive the sheer tribalism because it’s accompanied by deliberation—by discussion and thought. We fool ourselves into believing our ideas or our intellects are in control when it is often our identity or our history.

This doesn’t mean that group deliberation is always wrong. A collection of abolitionists who met and grew in dedication to the abolitionist cause in Boston in 1860 were right. Unquestionably they were right. But what it does mean is that like-minded group deliberation is suspect, and it can be suspect even in a righteous cause. “The ends justifies the means” is a concept born in unanimity and fervor.

When you survey our fracturing nation, you see a number of quite significant ideological and religious cocoons. I’ve mentioned one—the white Evangelical church. When 81 percent of its members are of like mind on a critical political issue, a bubble can form. But there are others. Did you know that entire American urban centers are more ideologically uniform than the white Evangelical church?

The island of Manhattan gave 87 percent of its vote to Hillary Clinton. The city of San Francisco voted for Clinton over Trump 84 percent to 9 percent. Hillary won 91 percent of the vote in Washington, D.C. Just ask dissenters, this level of unanimity breeds its own kind of self-righteousness and intolerance. It feeds its own kind of blindness.

The tidal pull of tribalism should humble us all. For many of us, it renders our virtue an accident of history and birth. For others, it gives our sin and vice a terrible momentum that’s so very hard to reverse.

Time and again I go back to the triple admonitions of Micah 6:8—“He has told you, O man, what is good; and what does the Lord require of you but to do justice, and to love kindness, and to walk humbly with your God.” It’s a verse for all time, but it also seems especially appropriate at this time.

Seek justice, yes. In a polarized time, that’s the easy command. That’s the call to fight for what’s right. The next two commands, however, come much harder, but their imperative is easier to understand when we know the truth that our virtue is often accidental. Our vices are stubborn. I can be kind to men and women who are confronting their own history and circumstance. And I must be humble. I must. Even (and perhaps especially) when I feel most confident.

In recent months I’ve come under a surprising amount of fire from the right for my commitment to civil liberties. I can write all day long about the value of the Bill of Rights as the indispensable component of the American social compact, but I’ve got a more selfish reason to preserve free speech and the marketplace of ideas: I might be wrong, and I need access to the truth.

I don’t want to trust the wisdom of my crowd or the assumptions of my own virtue. I’ve long pondered these remarkably honest words from Ta-Nehisi Coates, written almost nine years ago:

This basic extension of empathy is one of the great barriers in understanding race in this country. I do not mean a soft, flattering, hand-holding empathy. I mean a muscular empathy rooted in curiosity. If you really want to understand slaves, slave masters, poor black kids, poor white kids, rich people of colors, whoever, it is essential that you first come to grips with the disturbing facts of your own mediocrity. The first rule is this--You are not extraordinary. It's all fine and good to declare that you would have freed your slaves. But it's much more interesting to assume that you wouldn't have and then ask, "Why?" This is not an impossible task. But often we find that we have something invested in not asking "Why?" The fact that we -- and I mean all of us, black and white -- are, in our bones, no better than slave masters is chilling. The upshot of all my black nationalist study was terrifying -- give us the guns and boats and we would do the same thing. There is nothing particularly noble about black skin. And to our present business it is equally chilling to understand that the obstacles facing poor black kids can't be surmounted by an advice column.

Coates’s words apply not only to race, of course. Though Coates is openly atheist, he’s discussing a truth that a Christian should embrace—that we are not noble. We are shot-through with sin. When everyone around us is right, we deserve little credit for conforming. When everyone around us is wrong, we’re also likely to fail.

On this day, 155 years ago, the army of my ancestors folded its flags and stacked its arms. The tidal pull of tribalism carried away the men who gave me their name. Their legacy—and the legacy of every generation that has been caught up in the sweep of history in ways that harm us still today—should cause us all to pause.

When the crowd says yes, consider the option of no. When the crowd says go, discern whether we should stop. And through it all, pray for God’s grace—that we’re not too foolish to know the truth or to weak to do what’s right.

One last thing ...

A reader sent me this—a version of the old American folk hymn “Poor Wayfaring Stranger,” sung a cappella by Jos Slovick, from the film 1917. His version is haunting and beautiful. Enjoy:

Photograph of a Trump supporter and member of the antifa clashing by by Emily Molli/NurPhoto/Getty Images.