After the death of Kourosh, his son Cambyses II ascended the throne in 530 BCE. He inherited his father's plan to conquer Egypt, the last great independent power in the Near East. With a precise and well-planned campaign, Cambyses attacked Egypt in the year 525 BCE. This invasion was facilitated by the betrayal of some of Egypt's key allies, and the Persian army was able to achieve a decisive victory at the pivotal Battle of Pelusium, the gateway to Egypt.
After this victory, the city of Memphis, the capital of Egypt, was besieged and captured, and the Pharaoh of Egypt was taken prisoner. Thus, the ancient civilization of Egypt became one of the satrapies of the Achaemenid Empire. The historical image of Cambyses is heavily influenced by two contradictory narratives. Herodotus portrays him as a mad, ruthless, and impious king who insulted the sacred customs of the Egyptians.
This negative image is in sharp contrast with contemporary Egyptian and Persian evidence. Inscriptions show that Cambyses adopted all the titles of a pharaoh, respected local customs, and presented offerings to the Egyptian gods. This sharp contrast indicates that Herodotus's narrative is likely a reflection of a hostile tradition created and embellished by disgruntled Egyptian factions. In all probability, the "madness of Cambyses" is a historical slander.
According to the Behistun Inscription, which was written by Darius, Cambyses secretly had his full brother, Bardiya (Smerdis), murdered before his departure to Egypt to prevent any claims to the throne in his absence. In March of 522 BCE, while Cambyses was still in Egypt, a Magus named Gaumata usurped the throne by impersonating Bardiya and, due to actions such as forgiving taxes, gained widespread support throughout the empire.
Cambyses started back towards Pars to confront the usurper, but in the summer of 522 BCE, he died mysteriously in Syria. Herodotus attributes the cause of death to an accidental wound from his own sword, while Darius's inscription vaguely states that "he died his own death." This phrase could refer to suicide, an accident, or even assassination, leaving the mystery of his death unsolved.
The death of Cambyses plunged the young Achaemenid Empire into a deep succession crisis. In this power vacuum, Darius, a distant relative of Kourosh from a junior branch of the Achaemenid dynasty, along with six other Persian nobles, orchestrated a daring coup. They assassinated the usurper Gaumata in a fortress in Media, and Darius seized the throne for himself.
Many modern historians question Darius's narrative and believe that the person who rebelled was, in fact, the real Bardiya, and that Darius usurped power by staging a coup against the legitimate king and created the story of the "usurper Gaumata" to justify his own actions. This "Gaumata affair" is one of the most fascinating political mysteries of this period.
Darius's seizure of power was not met with public acceptance, and the first year of his reign was spent in a widespread civil war against nine "false kings" who had risen in rebellion throughout the empire. His final victory over these rebellions was a testament to his extraordinary military skill and set the stage for the extensive reforms that would bring the Achaemenid Empire to the peak of its power and glory.