What was Robert Duncanson's stimuli for the painting "The Land of the Lotus Eaters?

Robert Duncanson’s painting "The Land of the Lotus Eaters" conveyed historical, literary subjects. It was inspired by Tennyson’s poem about the paradise that seduced Ulysses’ soldiers. But in the painting, white soldiers are resting on the banks of a river while being served by the dark-skinned Americans, that the south had grown dependent on slave labor reflecting criticism.