On slavery, Mitchel remained uncompromising. As the South's manpower reserves depleted, Generals Robert E. Lee and Patrick Cleburne (a native of County Cork) proposed that slaves should be offered their freedom in return for military service. Although he had been among the first to claim that slavery had not been not the cause of the conflict but simply the pretext for northern aggression, Mitchel objected: to allow blacks their freedom was to concede that the South had been in the wrong from the start. His biographer Anthony Russell notes that it was "with no trace of irony at all", that Mitchel wrote: