ON Jan. 31, 1865, Congress passed the 13th Amendment, banning slavery in America. It was an achievement that abolitionists had spent decades fighting for — and one for which their movement has been lauded ever since.

But before abolitionism succeeded, it failed. As a pre-Civil War movement, it was a flop. Antislavery congressmen were able to push through their amendment because of the absence of the pro-slavery South, and the complicated politics of the Civil War. Abolitionism’s surprise victory has misled generations about how change gets made.

Today, diverse movements cast themselves as modern versions of the struggle against slavery. The former Republican senator Jim DeMint, now the president of the Heritage Foundation, claimed that small-government “constitutional conservatism” has inherited the cause; the liberal TV host Chris Hayes, writing in The Nation, said battling climate change was the “new abolitionism.” That term has become shorthand for “fighting the good fight.” But the long struggle against slavery shows how jerky, contingent and downright lucky winning that good fight was. 

It’s hard to accept just how unpopular abolitionism was before the Civil War. The abolitionist Liberty Party never won a majority in a single county, anywhere in America, in any presidential race. Ralph Nader got closer to the presidency. In 1860 the premier antislavery newspaper, The Liberator, had a circulation of under 3,000, in a nation of 31 million.

Even among Northerners who wanted to stop the spread of slavery, the idea of banning it altogether seemed fanatical. On the eve of the Civil War, America’s greatest sage, Ralph Waldo Emerson, predicted that slavery might end one day, but “we shall not live to see it.” ...