Why did the book say that Darius was more important as on administrator then as a conqueror?

Darius I is considered more important as an administrator than a conqueror because he effectively organized and managed the vast Persian Empire, implementing a system of provincial governance that allowed for efficient rule over diverse cultures. His administrative reforms, such as the introduction of standardized taxation and the establishment of a postal system, helped maintain stability and promote economic growth. While his military conquests expanded the empire's territory, it was his ability to govern and integrate these lands that ensured the long-term success and cohesion of the Persian state.