In 13 years, 9/11 had a museum. But six generations after emancipation, America’s “peculiar institution” had none. Enter John Cummings, a “rich white boy” and New Orleans real estate magnate. In December, he opened Louisiana’s Whitney Plantation, a museum solely about slavery. He won’t explain why he did it, but he’s won praise from experts and gasps from neighboring estates offering plantation picnics. Cummings is unapologetic about his provocative exhibits, including 60 ceramic heads of rebellious slaves on spikes. Maybe that’s why it’s taken so long.