The decline of the Mauryan Empire, which began after the death of Ashoka in 232 BCE, was caused by a combination of factors:
Weak Successors: Ashoka's successors were weak and incompetent rulers who could not hold the vast empire together.
Division of the Empire: The empire was partitioned into western and eastern parts after Ashoka's death, which weakened its unity.
Financial Crisis: The enormous expenditure on the army and the bureaucracy, along with large grants to Buddhist monks, strained the royal treasury.
Oppressive Provincial Rule: Provincial governors (amatyas) often became corrupt and oppressed the local population, leading to revolts.
Ashoka's Pacifist Policies: Some historians argue that Ashoka's policy of Dhamma and non-violence undermined the military strength and aggressive spirit required to maintain a large empire.
Brahmanical Reaction: The patronage of Buddhism by Ashoka and his anti-sacrifice policies antagonized the Brahmins, who may have contributed to the empire's downfall. The last Mauryan king, Brihadratha, was assassinated by his Brahmin commander-in-chief, Pushyamitra Shunga.
Vastness of the Empire and Communication Challenges: The sheer size of the empire made it difficult to administer and control from the center, especially with developing communication lines.