For what purpose did the Confederacy pass the "twenty-Negro law," which exempted from military service one white man on every plantation with twenty or more slaves?

Explanation:

Twenty Negro Law was a legislation passed during the civil war by confederate congress. It exempted one white male from serving in the military if they gave 20 slaves. Its purpose was to keep enough white males behind to prevent slave revolts especially after Lincoln announced Emancipation proclamation. The poor white Southerners  resisted this law. The majority of the Southern white males less than twenty slaves or none at all, they considered it as a system that allowed the wealthier  men to avoid service. Twenty Negro Law stayed in effect till 1865.