Slavery isn’t as formal or as widespread in the United States today as it was in the 1850s, of course, but it’s still easy to find. Go to backpage.com, the leading website for prostitution advertising and search for your hometown. Some of the women selling sex there are adults voluntarily in the business, but many are women or girls under the control of pimps who take every penny they earn, brand them with tattoos and beat them if they don’t earn enough.

Yet, in the United States, we typically arrest the victims rather than the pimps or the johns. Rectifying that would be a step toward modern emancipation.

The slavery index is the work of Andrew Forrest, an Australian billionaire who was awakened to the issue after his 15-year-old daughter, Grace, worked in an orphanage in Nepal. Grace later revisited the orphanage with her parents to check in on old friends — who were no longer there. They had, it turned out, been sold to brothels abroad.

After returning to Australia, Forrest ordered a review of his mining company’s supply chains to make sure that there was no forced labor. He promptly found that some overseas laborers had had their passports confiscated and had gone unpaid for years. “With slavery experienced by my family and in my business, it was everywhere if you looked,” he recalls, and he began a campaign against modern slavery.

Maybe we can find inspiration today not just from “12 Years a Slave,” but also from the anti-slavery movement that began in Britain in the 1780s. It was one of the first great human rights campaigns in the world.

People then simply accepted slavery. The Bible encouraged slaves to be obedient, the Church of England owned a major slave plantation in Barbados and Thomas Jefferson advocated powerfully for human freedom except where slaves were involved.

That British abolitionist movement, pioneered by Quakers and led by Thomas Clarkson and William Wilberforce, with help from a former slave named Olaudah Equiano, caught fire and changed the world. Some 390,000 people, more people than were then eligible to vote in Britain, signed petitions against slavery. Hundreds of thousands of people boycotted sugar made with slave labor. It’s a story movingly told by Adam Hochschild in his superb book “Bury the Chains.”

The abolitionists succeeded in ending the trans-Atlantic slave trade, but their work is not finished. I fear that a century from now, someone may put together a movie about slavery in 2013, leading our descendants to shake their heads and ask of us: What were they thinking?