@Kail
This is some of my favorite history, and I'm always happy to discuss it. Cannae was legendary for how ruinous it was to the Roman Republic, they lost almost an entire generation of young men in a single battle. Many historians point to how unique Rome was for being able to fight in any capacity afterwards, as it would have defeated any other country in the same time period. And the war thereafter consisted of the famous "Fabian tactics", where Roman field armies simply did not fight Hannibal on the open field since they could never afford another battle like that. This stategy worked, as Hannibal was recalled to Carthage before he could force the Romans into battle again.
During the period you speak of, the Second Punic War, the Roman army on the field of Cannae numbered 86,400 men, their total forces around the Empire were around 130,000. During the height of the Roman Empire their total soldiers scattered across the empire numbered 377,728 soldiers. This number was NEVER seen again in the West until Napoleon. The First Crusade consisted of only 100,000 soldiers AND non-combatants, and the best information I could find said the Holy Roman Empire was the only individual country that could muster anywhere near that many soldiers on its own. Feudal countries, such as the ones displayed in this manga, simply couldn't muster the numbers of men that more centralized states could (like Rome or Revolutionary France), nor did they have the population or resources to support so many men.
Napoleon once allegedly said to the Austrian minister Metternick "You cannot stop me. I can lose 30,000 men a month," to describe the massive losses the French were capable of taking. Even in the 19th century, 45,000 men was an enormous number of soldiers, every one of which represented a wealth of training and resources. That was also an era where armies had left behind the added expense of armor, that took blacksmiths months to forge, and the training required to wield an melee weapon or bow.
The only way a loss of 45,000 soldiers would be remotely believable would be if the Empire in this story was similar in size and structure to China during the period, which some historians believe was able to field half a million men. No nation of the Occident could come remotely close.
