Total War and Siege VS Justified

Total war is a stratagy where you burn down EVERYTHING.No mercy. kill everything that can help the enemy is that justified? Siege is where you cut off all supplies and wait until the enemy surrenders. Both of these are kinda cruel but siege at least gives them a little mercy. So in the civil war I think using siege is justified because after it never said that you can't give the civilians food after.  But total war is horrible and whoever does it is cruel.