We live in a chilling time for some outside mainstream Christian religious traditions. A presidential candidate feels free to declare that reading John F. Kennedy’s 1960 campaign speech in support of walling off church and state makes him “want to throw up” and Florida’s governor Rick Scott recently indicated he’ll sign a bill allowing “inspirational messages” (a transparent euphemism for prayer) at public school events because “I believe in Jesus Christ.” They are just the latest in a long line of individuals and groups who have been trying to bulldoze that wall since Thomas Jefferson wisely put it up in the Constitution. The first book length history of the only time in which American government officials forcibly expelled citizens from their homes solely on the basis of their religion reminds us why that wall needs regular shoring up.

In 1862, in the midst of the Civil War, General Ulysses S. Grant ordered every Jew in his military district covering a large section of the central Southern states to leave within 24 hours. He was trying with little success to control the enormously profitable and illegal trade in contraband cotton—much of it being carried out by his own officers—and took out his frustration on the Jews. Man, woman and child, many if not most Union loyalists, few if any involved in the cotton trade, faced a stark choice of packing whatever they could carry and heading off for distant and often unknown parts or military confinement. Many people lost everything they owned as they were driven, in some cases at bayonet point, from their homes.

Brandeis historian Jonathan D. Sarna’s powerful new book (Schocken/Next Books), When General Grant Expelled the Jews, retells this ugly, barely remembered yet surprisingly ultimately uplifting chapter in American history. The incident ultimately helped affirm the notion that no official state religion exists—for good reasons. Sarna’s wide-ranging and judiciously balanced book is the latest entry in the luminous Schocken/ Nextbook Jewish Encounters series. Each book thoughtfully pairs a great writer and an important facet of Jewish life, from Poet Laureate Robert Pinsky on the biblical King David to gritty journalist Douglas Century on the American boxing champion Barney Ross, in short, essayistic explorations.

The worst official anti-Semitic act in American history occurred on December 17, 1862. At the time, Grant, eventual commander of all federal forces, oversaw the Union army within a military district comprehending southern Illinois, most of Kentucky, western Tennessee and Mississippi. Cotton was in some respects the material cause of the war. The world wanted Southern cotton; slaves made the product available. The North still needed it. Enormous profit could be made, easily five-fold the price paid, by purchasing cotton bales from Confederate sources and selling them to Northern and English mills. The uncontrolled trade across the battle lines was a huge problem for the Northern armies: they were trying to conquer a rebellion while cotton sales provided Confederates rebels with money and supplies to sustain the fighting. Grant’s outraged subordinate General William Tecumseh Sherman complained to him, “We cannot carry on war and trade with a people at the same time.”

Profiteers of every stripe were involved in the contraband cotton trade, including many army officers. According to Sarna, some traders were Jews. They were mainly recent immigrants who moved about peddling goods to soldiers. One of those who also sought to trade in cotton, though, was General Grant’s father. The 68-year-old Jesse Grant sought out his powerful son in early December as an agent on behalf of a family of Cincinnati Jewish clothing manufacturers seeking a permit to purchase cotton.

Sarna speculates that Grant was frustrated that even his own father, a man with whom he already had a strained relationship, wanted to profiteer in cotton—albeit on behalf of Jewish merchants. He hastily wrote out an order banishing all Jews throughout his entire command. General Order No. 11 read:

1. The Jews, as a class, violating every regulation of trade established by the Treasury Department, and also Department orders, are hereby expelled from the Department. 2. Within twenty-four hours from the receipt of this order by Post Commanders, they will see that all of this class of people are furnished with passes and required to leave, and any one returning after such notification, will be arrested and held in confinement until an opportunity occurs of sending them out as prisoners unless furnished with permits from these Head Quarters. 3. No permits will be given these people to visit Head Quarters for the purpose of making personal application for trade permits. BY ORDER OF MAJ. GEN. U.S. GRANT

It’s difficult to say how many Jews—which officers carrying out the order interpreted to mean anyone born of Jewish parents—were banished, because fierce fighting in the district prevented the order from being fully implemented. Questions also arose as to whether Grant intended his order to include Jewish soldiers in the Union Army itself.

But families were, as the United Order Bnai B’rith Missouri Lodge protested, “driven from their homes, deprived of their liberty, and injured in their property without having violated any law or regulation. . . .” Among the worst actions, soldiers pushed the entire Jewish population out of Paducah, Kentucky, at least 30 households, and left their properties to be ransacked after they left.

For Jews who had fled centuries of persecution in the Old World, the New held the promise of freedom from governmental and military attack. And here it was once again.

For the first time, however, American Jews acted in a unified political manner to protest their treatment. President Abraham Lincoln received representatives of the people of Paducah in the White House. Likely apocryphal, a widely reported conversation between President Lincoln and the leader of the Paducah group linked Jews to ancient Israel and America to the Promised Land. Lincoln supposedly said, “And so the children of Israel were driven from the happy land of Canaan?”

To which the Paducah representative replied, “Yes, and that is why we have come unto Father Abraham’s bosom, asking protection.” And the President said, “And this protection they shall have at once.” The order was forthwith rescinded.

Grant quickly regretted General Order No. 11. After his election as president in 1868, he bent over backwards to demonstrate that it was an aberrant and thoughtless act done, he claimed, “without any reflection and without thinking of the Jews as a sect or race.” He emphasized, “I have no prejudice against sect or race, but want each individual to be judged by his own merit.”

In fact, his presidency inaugurated what Sarna refers to as a golden age for Jews in the country. Grant appointed more Jews to public office than any previous president. No other president until well into the 20th century so firmly urged clarity in keeping church and state apart nor made such efforts to promote freedom of religious expression and the embrace of non-Protestants and non-natives as fully American.

Perhaps influenced by remorse over his General Order No. 11, his views extended to foreign affairs. The United States had long kept its hands off other nation’s internal affairs. As a slaveholding land, America did not have a leg to stand on when it came to intervening in human rights elsewhere. But now, Grant for the first time chose to take an active stance regarding another nation’s oppression of its citizens, in this case government attacks on Jews in Romania. He appointed a Jewish American as consul to Bucharest “for the benefit of the people who are laboring under severe oppression.” In making the controversial appointment, he wrote that a nation that defends the freedom of all its citizens without regard to their religion or birth “naturally believe[s] in a civilization the world over which will secure the same universal liberal views.”

Grant also advocated a failed constitutional amendment requiring states to offer free public education for all children and barring those schools from teaching any “religious, atheistic, or pagan tenets” and prohibiting the use of school funds “for the benefit…of any religious sect or denomination.” So popular did Grant become among Jews that he was invited and became the first American president to attend Jewish worship services, at the dedication of a new Washington, D.C., synagogue. Sarna writes, ‘Now, the man who had once expelled ‘Jews as a class’ from his war zone personally came to honor Jews for upholding and renewing their faith.”

America has been fighting this ideological war over freedom of religion and freedom from an established state religion since the Pilgrims fled here to escape the strictures on their lives and religious practices imposed by the Church of England. Sarna’s brilliantly nuanced exploration of the worst official anti-Semitic incident in American history offers us a clear reminder in these ideologically fraught days why keeping up a firm wall between church and state remains a core defense for all of our freedoms.