When Alexis de Tocqueville visited the United States in 1831, he discovered a frightening schism along the Ohio River. On its right bank, the free state of Ohio teemed with industry and activity. “The fields,” he wrote, “are covered with abundant harvests. The elegance of the dwellings announces the taste and activity of the laborer, and man appears to be in the enjoyment of that wealth and contentment which is the reward of labor.” On the opposite side of the river, however, de Tocqueville was stunned by the idleness and underdeveloped character of slaveholding Kentucky.

In Ohio, the French observer concluded, labor was “honored” as a means of creating prosperity and improving one’s lot in life; in Kentucky, labor was “confounded with the idea of slavery,” seen as a vulgar and distasteful pursuit, only fit to be carried out by an underclass of bondsmen while their white overseers lazily reaped the benefits. The reliance on forced, black labor led white Southerners to shun hard work and undermined the ambition that powered the free states. It’s no wonder then that, at the start of the U.S. Civil War, the total population, manufacturing ability, and material resources of the industrious Northern states dwarfed their slaveholding Southern challengers by several magnitudes. “Slavery,” concluded de Tocqueville, “not only prevents the whites [of slave states] from becoming opulent, but even from desiring to become so.”

Thirty years later, another European was watching the unfolding drama between North and South, deeply concerned about what the U.S. Civil War could mean for the world’s laborers. Karl Marx had a soft spot for the United States. He felt that American representative democracy provided the greatest opportunity for the working classes to develop and exert their power. Marx allegedly considered immigrating to Texas, where many refugees of the German revolution of 1848—including his brother-in-law—had put down roots in the town of Sisterdale. (This town of progressive free-thinkers was later violently suppressed by Confederate irregulars.)

Though he never made the move, he did involve himself in American affairs, serving as the London correspondent for Horace Greeley’s New York Daily Tribune in the decade preceding the war. The Tribune was famous among Whigs and Republicans who shared its staunch abolitionist ideals. Marx’s critical reportage on European politics and labor issues fit in with the popular progressive maxim of the era, “free soil, free labor, and free men.” Among the many readers of the Tribune during this period was a young, up-and-coming politician named Abraham Lincoln.

In An Unfinished Revolution, author Robin Blackburn examines the influence that pre-war European radicalism had on the Union cause, the fascinating similarities and important contrasts in Lincoln and Marx’s political philosophies, and how labor activists carried the torch of emancipation into the post-war years. It’s a deeply researched, highly readable, thought-provoking book, though Blackburn’s insightful analysis comprises only the first hundred pages of the volume. The rest is made up of primary sources, meant to aid in the understanding of Lincoln, Marx, and other important voices of the time.

Blackburn views the U.S. Civil War and Reconstruction era through the lens of labor, and in particular focuses his narrative on the notion of free labor, as espoused by Lincoln’s Republican Party and Marx’s International Worker’s Association. As a young man, Lincoln experienced exploitation first hand; his martinet of a father would lend him out to others for work and retain all the income for himself. Once beyond his father’s control, the future president worked hard to better himself, raising himself from a backwoods afterthought to a prominent attorney and politician. “This background,” argues Blackburn, “reinforced his belief that the free labor system allowed a man to make his way in the world.” Growing up along the Ohio River, in Kentucky and Indiana, Lincoln undoubtedly saw the same stark contrast that struck de Tocqueville, and the hard lessons he learned there informed his later abolitionism.

From his distant vantage point in England, Karl Marx nevertheless had a decidedly clear view of what slavery meant for the concept of free labor. As long as some laborers toiled in literal chains, he believed, all laborers would be bound in metaphorical ones. From the very beginning he supported the Union cause, arguing that any attempt to pin the war on mere economic policy differences between North and South was hogwash—this was a slaveholder’s revolt aimed at preserving the vast wealth represented by slaves. For Marx, says Blackburn, the Civil War was “a decisive turning point in… history,” that would “set the scene for emancipation and be a great step forward for the workers’ cause on both sides of the Atlantic.”

We don’t know for sure if Lincoln ever read any of Marx’s writings in the Tribune, but we do know that Marx had a particular interest in the president, and that despite some misgivings about his handling of the war in the early stages, believed that he was an ally of the working man. On Lincoln’s reelection in 1864, Marx drafted a letter of congratulations to the president on behalf of the IWA, praising Lincoln’s resolve, and noting that the working men of Europe “consider it an earnest of the epoch to come, that it fell to the lot of Abraham Lincoln, the single-minded son of the working class, to lead his country through matchless struggle for the rescue of an enchained race and the reconstruction of the social world.” In an official acknowledgement conveyed via Ambassador Charles Francis Adams, Lincoln politely indicated that he found such support encouraging.

“In the post-Civil War era,” writes Blackburn, “The recently reunited United States was the most dynamic and soon the largest capitalist state in the world. No country illustrated Marx’s ideas with greater precision and purity.” With Lincoln’s assassination, the fate of the “reconstructed social world” he helped design was in doubt. Blackburn morosely explores the failure of Reconstruction and the chaotic post-war political world in which the pitched battle between labor and capital blazed out of control. Lincoln’s dream of free labor was drowned in Gilded Age excess, while progressive activists and labor leaders (including Marx’s IWA, now operating in the U.S.) struggled to keep their head above water. This is the titular “unfinished revolution,” the hope envisioned by Lincoln and Marx of a world of free men able to enjoy the fruits of their labor, quashed by the powerful oligarchy of robber barons who dominated the end of the 19th century.

Blackburn’s writing is taut, intelligent, and compelling. He packs an astonishing amount of information into a scant hundred pages, providing a fresh and powerful look at Civil War politics and social issues. An Unfinished Revolution is also valuable for its large appendix of primary sources, which includes not only relevant writings and lectures by Lincoln and Marx, but also scene-setting excerpts from Thomas Fortune’s classic Black and White and articles from the Woodhull & Claflin Weekly. Blackburn provides an amusing characterization of the latter publication’s editor, Victoria Woodhull, a free-loving, controversial progressive activist who the author calls “the Arianna Huffington of the 1870s.”

An Unfinished Revolution is a powerful account of an extraordinarily consequential moment in time, and a reminder that we still feel those consequences 150 years later. The revolution is still unfinished.