How do the empires of the second-wave civilizations differ from the political systems of the First Civilization?

The empires of the second-wave civilizations, such as the Roman and Persian empires, were characterized by more centralized bureaucratic structures and expansive territorial control compared to the city-states of the First Civilization, like Sumer and Egypt. Second-wave empires often employed complex administrative systems to manage diverse populations and vast territories, while the First Civilizations relied more on kinship ties and local governance. Additionally, second-wave empires utilized military expansion and trade networks to enhance their power and influence, whereas First Civilizations were more localized and focused on sustaining agrarian economies.