Just a few centuries ago, when you wanted to “sack another city/kingdom”, you had to do it through a siege. If you don’t know what a siege is, it’s basically when you get an army, and some massive tools, to mow down the city defenses of an opponent, before taking it over.
Those war techniques have obviously been rendered useless through the existence of missiles and airplane bombing. Nevertheless, we’re not discussing this for the sake of “war practicality”. Our focus here is on understanding history warfare, and how it evolved into what it is now.