"We love being the country that freed the slaves," says historian David Blight. But "we're not so fond of being the country that had the biggest slave system on the planet." That's why Blight was glad to see the new film 12 Years a Slave, an adaptation of an 1853 memoir by Solomon Northup. Northup was a free black man who was kidnapped into slavery in 1841 and won his freedom 12 years later. "We need to keep telling this story because it, in part, made us who we were," Blight tells Fresh Air's Terry Gross...