Final answer:
Darius came to power after leading a conspiracy and assassinating Cambyses' younger brother. He then worked to consolidate royal power and improve the infrastructure of the Persian Empire.
Step-by-step explanation:
Darius came to power in 522 BCE after leading a conspiracy that assassinated Cambyses' younger brother Bardiya, who had briefly ruled. Once Darius seized the throne, he worked to consolidate royal power and improve the infrastructure of the Persian Empire. He expanded the empire, established a postal service, and standardized weights, measures, and coins.