Among the enduring mysteries of the American Civil War is why millions of Northerners were willing to fight to preserve the nation’s unity. It is not difficult to understand why the Southern states seceded in 1860 and 1861. As the Confederacy’s founders explained ad infinitum, they feared that Abraham Lincoln’s election as president placed the future of slavery in jeopardy. But why did so few Northerners echo the refrain of Horace Greeley, the editor of The New York Tribune: “Erring sisters, go in peace”? The latest effort to explain this deep commitment to the nation’s survival comes from Gary W. Gallagher, the author of several highly regarded works on Civil War military history. In “The Union War,” Gallagher offers not so much a history of wartime patriotism as a series of meditations on the meaning of the Union to Northerners, the role of slavery in the conflict and how historians have interpreted (and in his view misinterpreted) these matters. The Civil War, Gallagher announces at the outset, was “a war for Union that also killed slavery.” Emancipation was an outcome (an “astounding” outcome, Lincoln remarked in his second Inaugural Address) but, Gallagher insists, it always “took a back seat” to the paramount goal of saving the Union. Most Northerners, he says, remained indifferent to the plight of the slaves. They embraced emancipation only when they concluded it had become necessary to win the war. They fought because they regarded the United States as a unique experiment in democracy that guaranteed political liberty and economic opportunity in a world overrun by tyranny. Saving the Union, in the words of Secretary of State William H. Seward, meant “the saving of popular government for the world.”

more from Eric Foner at the NYT here.