Micah Xavier Johnson, who killed five police officers in Dallas, was increasingly drawn to black nationalist ideology and attended several meetings of the People’s New Black Panther Party. Gavin Eugene Long, who killed three officers in Baton Rouge, said he belonged to the Washitaw Nation, an obscure black nationalist group that claims ownership to the huge swath of the United States obtained in the Louisiana Purchase on the belief that they are descended from a U.S. indigenous group.