The term has also been applied retroactively to dominant states of the past. In her book Day of Empire, American professor Amy Chua suggests that the Achaemenid Empire, the Tang dynasty, the Roman Empire, the Mongol Empire, the Dutch Empire, and the British Empire were successful examples of historical hegemons; the Spanish Monarchy, Greater East Asia Co-Prosperity Sphere, and Third Reich were counters; and she reflects on assertions that the United States is a modern hyperpower. In a historical context, it is usually understood to mean a power that greatly exceeds any others in its political environment along several axes; Rome did not dominate Persia, Ancient India or China, but did dominate the entire Mediterranean area militarily, culturally, and economically.[16]