When John Wilkes Booth killed President Abraham Lincoln at Ford’s Theater in Washington on April 14, 1865, was he inspired by John Brown, the militant abolitionist whose public execution Booth had witnessed in Virginia six years earlier?

At first glance, the idea seems improbable. Ideologically, Booth and Brown were light-years apart. Booth was a Southern white supremacist who detested the notion of freedom and citizenship for black people. Brown, an antislavery Northerner, wanted America’s four million enslaved people to be emancipated immediately and integrated into mainstream society. Yet, in spite of this enormous difference, Booth had great admiration for Brown. Why?

It’s an issue that may hold the key to understanding the assassination of Lincoln. Booth and Brown—and, surprisingly enough, Lincoln himself—were conjoined on a deep level by what in that era was called “the higher law.” They were inclined to follow the dictates of the higher law—moral or religious principle—rather than human law. Reconsidering Booth’s murder of Lincoln in light of John Brown and the higher law leads to troubling questions. When is violence in the name of a higher cause justified, and when is it not? Can we distinguish between bad terrorism and good terrorism?

Brown, Booth, and Lincoln all appealed to a higher cause to justify taking up arms against what they viewed as a great social evil. Brown, a devout Calvinist, considered himself God’s chosen instrument for eradicating slavery. In 1856, he and several followers murdered five proslavery settlers in Kansas Territory to preserve that area for freedom. Three years later he invaded Harpers Ferry, Virginia with a band of 21 in a bold but futile effort to spark slave insurrections throughout the South that he hoped would lead to the fall of slavery. Instead, he was captured in Harpers Ferry, brought to trial, convicted of treason, and, on December 2, 1859, hanged publicly in front of rows of Southern soldiers. As Brown mounted the scaffold, he was calm and unruffled. He believed he was a divinely-appointed martyr for the antislavery cause.

His courage in the face of death made a profound impact on John Wilkes Booth, a 21-year-old actor. Booth had interrupted his engagement at a Richmond theater to join a militia company that stood with the troops near Brown’s scaffold. For Booth, Brown was a bold, dignified man who, though misled in his views, willingly sacrificed himself for a higher ideal. “He was a brave old man,” Booth said. In contrast, Lincoln was for Booth a scheming, power-hungry politician. Lincoln, Booth declared, was “made the tool of the North to crush out, or try to crush out slavery”; he was a “Sectional Candidate” intent on “overturning this blind Republic and making himself a king.” For Booth, Lincoln and other antislavery politicians were duplicitous and treacherous. In 1860, as he witnessed the rise of Lincoln and his fellow antislavery Republicans, Booth wrote that John Brown was far nobler than Lincoln, since, in Booth’s words, “open force is holier than hidden craft.”

The four years of civil war that followed Lincoln’s election drove Booth to draw an even sharper contrast between Old Abe and Old Brown. In a letter of December 1864, shortly after Lincoln was elected to a second term, Booth wrote bitterly of the president: “He is standing in the footprints of old John Brown, but no more fit to stand with that rugged old hero—Great God! No. John Brown was a man inspired, the grandest character of this century!” Lincoln, in contrast, was deceitful, tyrannical, and filthy-minded. “This man’s appearance,” Booth wrote, “his pedigree, his low coarse jokes and anecdotes, his vulgar similes, his frivolity, are a disgrace to the seat he holds.”

What really infuriated Booth was his conviction that America was now destined to be ruled by a dictator, Lincoln, who would bring about a horrible racial reversal. Booth, who referred to black people as “monkeys,” “apes,” or “thick-skulled darkies,” wrote that “this country was formed for the white not for the black man,” and that slavery was “one of the greatest blessings that God ever bestowed upon a favored nation.”

Booth’s anger boiled over on April 11, 1865, when he attended a speech in which Lincoln called for suffrage for certain African Americans—the first time an American president had ever done so. Booth growled, “That means nigger citizenship. Now, by God, I’ll put him through. That is the last speech he will ever make.” Privately, Booth declared that something “great & decisive” had to be done.

Three days later, Booth killed Lincoln. He was driven by what he saw as a patriotic and religious duty to save his nation from racial integration through an act of violence—exactly what John Brown had done, but in reverse. Brown had changed history in single stroke, like the despot-killing Brutus or many other Shakespearian characters Booth had played. Booth thought that he too could play hero on the national stage. Who knew? Perhaps by shooting Lincoln he would become even grander than the man he called “the grandest man of the century,” John Brown. Like Brown’s letters and speeches, Booth’s writings are full of firmly proclaimed devotion to God and country. Just as Brown saw himself as a patriot acting in the spirit of 1776, Booth looked back fondly on the American Revolution and wrote, “How I have loved the old [American] flag, can never now be known.” If Brown saw his violent deeds as God-directed, so did Booth, who scribbled in his pocket diary shortly before he was captured in a Virginia barn, “God simply made me the instrument of his punishment.”

And so, both Brown and Booth followed the higher law. But can either of them be said to be justified in his actions? In Booth’s case, the answer seems a definite “no.” There has, however, been a long tradition of Booth-worshipping, from avid relic-gatherers just after the assassination to the ex-Confederate colonel Robert H. Crozier, who in his 1869 novel The Bloody Junto compared Booth to the worthiest “ancient semi-gods,” to the Confederate veteran Joseph Pinkney Parker, who in 1904 erected a monument with the words, “In honor of John Wilks [sic] Booth/For killing old Abe Lincoln,” to Izola Forrester, allegedly the granddaughter of Booth, who wrote in a 1934 book that “you cannot but feel a deep love for [Booth],” to the Southern shock jock and former Rand Paul aide Jack Hunter, who said that he personally raised a toast on every May 10, Booth’s birthday, to Lincoln’s assassin, about whom Hunter declared, “John Wilkes Booth’s heart was in the right place.” That kind of attitude led Erik Jendresen, the Executive Producer of the television movie Killing Lincoln, to remark that John Wilkes Booth “could be the poster child for the Tea Party.”

As for John Brown, many people today, including a few widely-read commentators—such as Tony Horwitz, Christopher Benfey, and Sean Wilentz—consider him a fanatical, perhaps insane, homegrown terrorist. But Brown was held in the highest esteem by some of America’s most thoughtful observers. Henry David Thoreau compared him to Jesus Christ, Harriet Beecher Stowe called him the greatest American, Frederick Douglass declared, “I could live for the slave, but he could die for him,” and W. E. B. Du Bois wrote, “John Brown was right.”

The contradictory responses to Booth and Brown, make it tempting to conclude that one person’s terrorist is another’s freedom fighter. But the picture gets more complicated—and more suggestive—when we recognize that Lincoln also advocated extreme violence in the name of higher ideals. Initially, he had dissociated himself from John Brown, declaring that while Brown’s motives were worthy, his actions were illegal. But as the Civil War wore on, he deemphasized law and precedent in pursuit of his goal of eradicating slavery. He used his presidential military powers to suspend habeas corpus and other civil liberties, and he directed his leading generals, Grant and Sherman, to pursue a brutal, scorched-earth strategy that some historians see as “total war.” And he did so in the name of God. Although Lincoln never joined a church, he read the Bible often, put “In God We Trust” on the nation’s currency, approached his Cabinet about the possibility of amending the Constitution to include mention of God, and issued an extraordinary nine proclamations of prayer, fasting, or thanksgiving in order to fire the North with spiritual enthusiasm.

In his second inaugural address in March 1865, Lincoln appealed to the Old Testament God to vindicate bloody violence in the battle against injustice. Only 750 words long, the speech contained fourteen mentions of God, three invocations of prayer, and four Biblical citations, including Lincoln’s militantly pious declaration: “If God wills that [the war] continue until all the wealth piled by the bondsman's two hundred and fifty years of unrequited toil shall be sunk, and until every drop of blood drawn with the lash shall be paid by another drawn with the sword, as was said three thousand years ago, so still it must be said ‘the judgments of the Lord are true and righteous altogether.’” John Brown would have agreed completely.

And so, on the fateful evening of April 14, 1865, three forms of higher law mingled explosively: that of Brown, who inspired Booth, though from the opposite vantage point of racial equality; that of Booth, who believed God-backed terrorism could preserve white supremacy; and that of Lincoln, who cited “the judgments of the Lord” to promote a holy war against slavery. Of the three, Lincoln has of course been best received by history, and we can say that his form of higher law—channeled as it was through American institutions like the electoral process and presidential proclamations—is indeed the most admirable. The loose-cannon higher law actions of Brown and Booth seem out of bounds, for these men acted outside of institutions, without the sanction of some larger group. To be sure, both Brown and Booth, by turning to violence, succeeded in galvanizing change. Brown did become a martyr in the North and was a major inspiration to Union troops as they marched southward, singing their favorite song, “John Brown’s Body,” quickly adapted by Julia Ward Howe as “The Battle Hymn of the Republic.” That’s why many antislavery leaders attributed the fall of slavery largely to John Brown’s heroic example.

John Wilkes Booth likewise succeeded in creating a martyr whose memory would transform the nation, only not the one he intended. The poet Walt Whitman considered the assassination of Lincoln the greatest boon to America, since it unified a nation whose deep divisions had created unimaginable bloodshed and suffering. Shared sorrow over the tragic death of  America’s “great Martyr Chief,” Whitman wrote, provided “a cement to the whole people, subtler, more underlying, than anything in written constitution, or courts or armies”; it was the one thing needed only to “really, lastingly condense—a Nationality.” Time has proved Whitman right. Lincoln since his death 150 years ago has been a unifying figure in the national consciousness, virtually the only constant amid shifting political winds and economic conditions—the most beloved of Americans among both conservatives and liberals.

But Lincoln is not just a unifying national icon. He is a lasting example of the proper use of the higher law: that is, the principled pursuit of justice through a popularly elected government. Although lone-wolf higher-law types like John Brown and John Wilkes Booth sometimes have positive results, history has shown that the higher law of individuals can also be a slippery slope that leads to unleashed violence. At Gettysburg, Lincoln announced “a new birth of freedom” for “this nation, under God”—a higher law declaration. But in the next breath he expressed a firm commitment to preserving “government of the people, for the people, by the people.” Even the most apparently virtuous aims, Lincoln knew, can be dangerous if they are not channeled through a democratically chosen government.

Here, in his address at Gettysburg, Lincoln defined the truly American higher law.