What Civil War officer proposed these terms to his opponent: "If you surrender you shall be treated as prisoners of war, but if I have to storm your works you may expect no quarter"?..... Confederate General Nathan Bedford Forrest routinely issued this warning to opposing forces and often received his desired result as he and his cavalry were feared throughout the Union Army.
Forrest fought a distinctly different type of war than the ordinary conflict between armies. He was not truly "cavalry"; he was a sort of "mounted infantry". He also almost always fought alone so he had no further resources to throw into any battle. He prevailed with what he had or he was forced to withdraw. So it is not unusual that he made that demand because he didn't have an unlimited source of manpower at his disposal and losing men in an assault clearly weakened him for the next encounter with the enemy. He was not, therefore, willing to lose manpower in a situation where the enemy knew that they could resist him without consequences.
In the same sort of situation - albeit from the other side - Mosby and other northern Virginia partisans treated their prisoners well. To have fought under the black flag as was the way of independent units in the Western theater would have simply increased the ferocity of resistance. If you're going to die anyway, you might as well fight. However, if you know that you will be well treated, it's always better to surrender and possibly live to fight another day.
Both of these strategies were designed to lower the casualty rate of the Confederate forces involved. Surrender or die in Forrest's case and surrender and live in Mosby's.
