The answer is because they grew the food. All humans require food, thus, there needs to be people who gather the food and where does that food come from? The peasants! Any empire, army, and country needs workers to grow food for their leaders, the soldiers, and everyone else. Any military, no matter how many men, the strength or skill of them cannot fight without food. No empire cannot survive and keep its citizens alive without food. Likewise, no country can survive without any food.