By KEVIN BAKER     JAN. 28, 2015

“I dreaded the approach of summer, when snakes and slaveholders made their appearance,” wrote Harriet Jacobs, author, educator, servant, mother of two — and escaped slave.

Jacobs had fled from Edenton, N.C., to get away from the attentions of the father of a little girl who “owned” her. These had persisted even after she had two children by another white man (and a member of Congress), so she “hid in a small crawl space above her free grandmother’s kitchen in the town” for seven years, as Eric Foner informs us in his illuminating new history, “Gateway to Freedom.” Eventually, passage north was secured on a ship with a “friendly captain,” and Jacobs settled in New York City. But as an escaped slave, she was never really secure anywhere in the United States, especially after passage of the Fugitive Slave Act, part of the Compromise of 1850. When, after 10 years of freedom, she learned that her owner “was making preparations to have me caught,” she fled again, to Boston, where abolitionist feeling was higher than in New York, which had long been debased by bigotry and the dollar into more pro-Southern sympathies.

It may seem difficult to believe that slave owners and hired slave catchers prowled the streets of Manhattan before the Civil War, openly carrying whips, pistols and manacles in order to reclaim their “property,” but such was the case. They “entered black churches during Sabbath services looking for runaways, and broke into blacks’ homes and carried them off without legal proceeding,” Foner tells us. Fugitive slaves in the city, wrote the Southern-born abolitionist Sarah Grimké, were “hunted like a partridge on the mountain.”

Unsurprisingly, the men who would make their living in this way were not terribly scrupulous about just which black face they decided to seize upon. Once the slave trade from Africa was banned in 1808, and as slavery in the North was slowly wound down, “an epidemic of kidnapping of free blacks, especially children,” occurred all over the Northeast. After the new federal statute of 1850 was passed, Foner writes, “the abolitionist William P. Powell departed for England with his wife and seven children, although no member of the family had ever been a slave.”

The 1850 law — supported by some of the most illustrious figures in congressional history, and hailed as vital for preserving the Union — was particularly odious. It rendered null and void the longstanding state “personal liberty” laws that had been used to declare runaway slaves free in the past, and provided “severe civil and criminal penalties for anyone who harbored fugitive slaves or interfered with their capture.” Special commissioners were given the final say on all fugitives, along with a financial incentive — $10 a head! — to decide in favor of the slave catchers. Federal marshals could deputize anyone they wished or “call on the assistance of local officials and even bystanders” to help in apprehending suspected runaways.

In other words, the new law would corrupt all citizens into aiding and abetting America’s great moral crime. But as Foner explains, fugitive slave laws were part of the warp and woof of the country from the very beginning, dating back to the 17th century in colonial New York. The Northwest Ordinance of July 1787 held that slaves “may be lawfully reclaimed” from free states and territories, and soon after, a fugitive slave clause — Article IV, Section 2 — was woven into the Constitution at the insistence of the Southern delegates, leading South Carolina’s Charles C. Pinckney to boast, “We have obtained a right to recover our slaves in whatever part of America they may take refuge, which is a right we had not before.”

Resistance to this sprang up in societies for manumission, and sometimes for the “colonization” of freed slaves back to Africa. But as it became clear that slavery was not going to die the natural death that had been devoutly wished for, “vigilance” and antislavery committees were set up. They came to form the Underground Railroad, a loose network of black and white individuals intent on actively helping slaves gain freedom (only in Canada was it truly secure) and evade recapture.

Foner, who as one of our leading historians has written or edited 24 books, including the Pulitzer Prize-winning “The Fiery Trial: Abraham Lincoln and American Slavery,” does a superb job of focusing the story of the Underground Railroad on a human level. He makes vivid the incredible risks and hardships so many slaves were willing to endure for their freedom, and how much it meant to them. They came by ship and by train, by horse and foot; by ways however arduous and ingenious. One William Jordan, it was reported, lived for 10 months in the woods, “surrounded by bears, wildcats, snakes, etc.” — although he “feared nothing but man.” Henry (Box) Brown had himself packed into a box three feet long, and shipped from Richmond to Philadelphia. The journey took almost 24 hours and nearly killed him, but according to eyewitness accounts, he stepped out of the box “with a face radiant with joy,” and began to sing a “hymn of praise.”

Foner also performs an invaluable service in restoring the record of liberated blacks who helped their fellow African-Americans to freedom. Here are, among many others, not only the legendary Harriet Tubman — who more than lives up to the legend — but also Louis Napoleon, an illiterate porter and window washer who “was credited with having helped over 3,000 fugitives escape from bondage”; the indefatigable David Ruggles, a freeborn black man who specialized in plucking slaves off ships in New York Harbor; and the anonymous crowds of free blacks, men and women, who rushed again and again to rescue fugitive slaves in violent street battles. On one occasion in Pennsylvania, they even killed a slave owner.

The penalties for whites helping the Underground Railroad could be severe, including mob assaults, tar-and-­featherings, the destruction of their careers, lengthy prison sentences and even the fatwa that the parish of East Feliciana, La., put on the head of the white abolitionist Arthur Tappan, offering the immense sum of $50,000 for his “delivery.” But none of it equaled what blacks stood to lose if caught down South trying to free their brothers and sisters. They were not deterred. “I shall have the consolation to know that I had done some good to my people,” Tubman replied when asked by a white abolitionist how she would feel if she were to be caught and put back into slavery.

Pitted against white mobs, hostile magistrates, policemen eager to claim rewards and the nearly demonic persistence of slaveholders looking to reclaim their property, the little band of men and women who ran the Underground Railroad were able to rescue “somewhere between 1,000 and 5,000 per year between 1830 and 1860.” Although this was a small number set against a total slave population approaching four million, such resistance, as Foner shows, was able to leverage the greater prize. The Underground Railroad infuriated the South, providing “the immediate catalyst” for the Fugitive Slave Act, which became in turn “a source of deep resentment in much of the North,” when armed ruffians started showing up in Northern towns and cities to drag away people’s friends and neighbors. The South, The New York Times noted in 1859, had made “the doctrine of state rights, so long slavery’s friend, . . . its foe,” poisoning relations between the sections until, as Foner concludes in this invaluable addition to our history, “the fugitive slave issue played a crucial role in bringing about the Civil War.”

GATEWAY TO FREEDOM

The Hidden History of the Underground Railroad

By Eric Foner

Illustrated. 301 pp. W. W. Norton & Company. $26.95.

Kevin Baker is the author, most recently, of the historical novel “The Big Crowd.”