Still, you raise an important point. Armies in Westeros (and elsewhere in the known world) are, by and large, armed gangs. The foot soldiers are often largely made up of peasants, gang-pressed by their lords into service for little-to-no pay and sent to die many miles from home. The liberty to sack a city or a village is essentially how these armies are paid. In this preindustrial society, commoners produced the food, textiles, and other items necessary for war, in addition to providing the levies that made up the infantry. Therefore, attacks on civilians were, by and large, considered fair game. In this world, war crimes—murder of civilians, the burning of villages, mass theft, rape—are endemic and acknowledged, occasionally with regret, as the cost of battle. The difference with Dany—aside from the massive scale of the dragon-fueled destruction—is that the carnage happened on camera, unlike events from the history of Westeros or those that happened largely out of our sight.
For instance, Tywin Lannister infamously allowed his troops to sack King’s Landing at the end of Robert’s Rebellion. In the books, Jorah, in the speech that includes the famous “there is a savage beast in every man” line, tells Dany:
Babes were butchered that day as well, and old men, and children at play. More women were raped than you can count.
But we should not limit these acts to characters we consider “villains.”
Robb Stark was a brilliant and honorable battle commander. Yet in the books, after his victory at the Battle of Oxcross in the Westerlands, he ordered his troops to pay “the Lannisters back in kind for the devastation they’d inflicted on the Riverlands.” This is Robb’s answer to Ser Gregor the Mountain Clegane’s activities, which included the murder and torture of civilians and the burning of villages and fields. And, in the show, it is the forces of Roose Bolton, Robb’s bannerman at the time, who nearly rape Brienne.
This is in no way an excuse for Dany’s actions. The mass murder and abuse of civilians, which she sparked by ordering Drogon to engage after the city bells had been rung, was horrendous. However, we must also acknowledge that warfare in the world of Game of Thrones leaves no one’s hands clean, even our most heroic characters. As the Hound said to Sansa in Season 2, “Stannis is a killer. The Lannisters are killers. Your father was a killer. Your brother is a killer. Your sons will be killers someday. The world is built by killers. So you’d better get used to looking at them.”