Adam Hochschild begins “Bury the Chains” (Houghton Mifflin, 432 pages, $27), his history of the movement to abolish slavery in the British Empire, by conjuring a world where “freedom, not slavery, was the peculiar institution.” In the 18th century, the majority of the world’s population was held in some kind of bondage. Only in a few parts of the Western world, above all in England and America, did freedom seem like the birthright of even the laborer and the peasant.

Yet it was in England and America, ironically, that slavery assumed one of its most brutal forms: the African slave trade, which over the centuries forced some 10 million people onto what Mr. Hochschild memorably calls “a vast conveyor belt to early death.”

Of all the places an African slave could end up, the worst was a sugar plantation in the Caribbean. Some 60% of all slaves brought across the Atlantic went to the sugar islands, which were the most lucrative of the European colonies.(In 1773, Mr.Hochschild notes, Britain imported five times more from Jamaica alone than from all its North American colonies put together.) But this profit was literally drawn from the blood of slaves, who were worked to death in the Caribbean as surely as any prisoner in a concentration camp. One statistic tells the whole story: When slavery ended in the British West Indies, Mr. Hochschild writes, “total imports of two million left a surviving slave population of only about 670,000.” The missing population, as measured in captives themselves and their nonexistent offspring, was the price of British slavery.

There can be no doubt that the abolition of this trade was one of the great accomplishments of the modern age. In “Bury the Chains,” Mr. Hochschild – whose last book, “King Leopold’s Ghost,” described the exploitation of the Belgian Congo – writes about the abolition movement in unambiguously moral terms. It becomes the tale of a few good activists triumphing over indifference and vested interest, driven solely by their commitment to an abstract ideal of human rights. The British abolition movement was, Mr. Hochschild writes, “something never seen before: it was the first time a large number of people became outraged, and stayed outraged for many years, over someone else’s rights.” Mr. Hochschild urges us to make his heroes our role models: “their passion and optimism are still contagious and relevant to our times.”

The result of this frankly hortatory impulse is a passionate and informative book, but also a limited one. Oddly, “Bury the Chains” seems at once old-fashioned – in its tendency to see history as the stage on which a few exceptional individuals play out their destinies – and anachronistically modern – in its unwillingness to acknowledge that the ideals and motives of the 18th century were not our own.

Mr. Hochschild dates the origin of the abolition movement to May 22, 1787, when a dozen men gathered in a London printer’s shop for “a Meeting held for the Purpose of taking the Slave Trade into consideration.” Their moving spirit was Thomas Clarkson, a young clergyman, who had decided in a road-to-Damascus moment to dedicate his whole life to the cause. Most of his allies at that first meeting were Quakers, members of the only sect in England then committed to ending slavery. But Clarkson and company quickly turned the tide of public opinion, inventing, as Mr. Hochschild notes, many of the tools that are still staples of political activism: leaflets, letter-writing campaigns, lobbying, even logos. (The image of a bound slave, with the caption “Am I Not a Man and a Brother,” quickly became the icon of the movement.)

Mr. Hochschild goes on to detail the progress and setbacks of the campaign, which finally resulted in the end of the slave trade in 1807 and the emancipation of all British slaves in 1833. He shows how the French Revolution and a series of slave insurrections in the Caribbean alternately hindered and helped the cause. And he details the parliamentary maneuvers, led by William Wilberforce, which translated Clarkson’s passion into concrete legislative achievements. At the same time, Mr. Hochschild draws vivid portraits of what life was actually like for all the participants in the slave economy – slaves, sailors, and ships’ captains, plantation owners and soldiers.

In his admiration for activists like Clarkson, however, Mr. Hochschild neglects the two larger factors that were indispensable for the success of their campaign. The first was religion, the evangelical Christianity that led so many clergymen to embrace the abolitionist cause. Mr. Hochschild acknowledges this motivation, but with discomfort and distaste, frequently mocking the religious scruples of Wilberforce and other members of the high-minded “Clap–ham Sect.” He would much prefer to cast the abolition movement as, in the words of his subtitle, a secular “human rights crusade”: “they placed their hope,” he writes on his last page, “not in sacred texts, but in human empathy.”

Yet it is certain that most of the British abolitionists, like their American counterparts decades later, would have named Christianity as the source of their convictions and the fuel for their ardor. Indeed, it’s doubtful whether any great philanthropic movement, from Clarkson’s to Martin Luther King’s, has ever succeeded without drawing on a fundamentally religious spirit. This may be an uncomfortable lesson for modern, secular liberalism, but it is a hard one to avoid.

Rather less edifying, but probably still more important, was the second factor Mr. Hochschild glosses over: the changing economics of slavery. He admires the British for abolishing slavery when “none of them gained a penny by doing so, and their eventual success meant a huge loss to the imperial economy.” But it is no coincidence that the abolition movement arose at the time and in the place where the Industrial Revolution was most advanced. The decline of mercantilism and the rise of free trade made Britain’s sugar plantations, for the first time, economically dispensable; only then could they be dispensed with on moral grounds.

“Bury the Chains” shows that passionate, dedicated individuals are necessary if justice is to prevail. Unfortunately, it cannot prove that they are sufficient.