—and in Old Testament times , the standard was same as Joshua did after winning the battle of Jericho—kill everything that walked or crawled in the loser’s fortress-—
Historically, in say the Bronze age, the majority of casualties occurred
when one side was forced to retreat and their undefended
rear was exposed to the killing zone.
This type of action found a renewal in fast moving
armored warfare, where the attackers could move faster
than those retreating.