Can you point me to scripture(s) that explains whether war is good or bad and if there are instances where it is blessed by God? What determines this?
God has authorized and participated in wars that were either designed to punish men for disobedience or protect His people from their enemies. Sometimes it was both at once. For example in the conquest of the Promised Land God said that He was using Israel as an instrument of His judgment after the Canaanites refused to repent and return to him even though he had given them 400 years to do so. (Genesis 15:16, Deut. 9:1-6)