Why did union general Benjamin butler declare enslaved African American refuges to be contraband or captured war supplies?

Union General Benjamin Butler declared enslaved African American refugees as "contraband" based on the military necessity to undermine the Confederacy's labor force. By classifying them as captured war supplies, he aimed to prevent their return to enslavers and provide them protection, thereby advancing the Union's war efforts. This decision also signaled a shift in the Union's approach to slavery, recognizing the potential of enslaved individuals to contribute to the Union cause.