Readers will not find a Marxist interpretation of the American Civil War laid out in this volume. Rather, they will observe Marx and Engels working to define their own approach to history and politics while analyzing the American Civil War as it developed into the greatest social revolution that the United States has so far achieved.

Radicals and revolutionaries found themselves in a complex political position at the outbreak of the American Civil War of 1861-65. They demanded a war against slavery as an evil in itself and as the root cause of the Confederate rebellion, but the Lincoln administration proclaimed it fought only to preserve the Union and would not interfere with slavery in the states where it already existed. "All knew," in the words of Lincoln's 1864 second inaugural address, that slavery "was somehow the cause of the war," but if, and to what extent, the war would end slavery and transom the country that had grown wealthy from the labor of four million enslaved African Americans remained an open question.

By the time the war ended in 1865, the radicals and revolutionaries got their way, thanks in large part to the actions of the enslaved themselves, and the North thus won a war that had also become a revolution against slavery.