Collateral damage before the ages of strategic bombing and artillery usually consisted of stuff like famine, fire, and exposure. Not that any of the militaries of the time really gave a flying fig. War back then was more along the lines of national scale murder rather than the extension of politics by force. Collateral damage is a new concept that originated during Vietnam. Before then it was just "War", "Burn the Heretic", and "Don't hurt the new slaves!"