Sudden Change in the Situation

The more primitive the battle, the simpler and more violent it would be. Battles purely for the sake of survival or revenge would always be the cruelest and bloodiest. These battles would be far simpler and more direct compared to barbarians' fights against wild beasts. The primitive rules of blood revenge dictated that cruel battles between barbarian tribes would have no innocents surviving.

Yet, in modern warfare of my original world, battles actually had both international rules and unstated rules, such as normal scale warfare, forbidding the use of large-scale AOE weapons like nuclear bombs, limited-fly zones, international treaties, and so on…