Mauryan Empire began to decline after the death of Ashoka in 232 BC. The last king was Brihadratha was assassinated in 185 BC-183 BC by his general Pushyamitra Shunga who was a Brahmin. The decline of the Maurya Dynasty was rather rapid after the death of Ashoka/Asoka. One obvious reason for it was the succession of weak kings.
The Mauryan Empire was divided into four provinces with the imperial capital at Pataliputra. From Ashokan Edicts, the name of the four provincial capitals were Tosali (in the east), Ujjain in the west, Suvarnagiri (in the south), and Taxila (in the north). At the centre of the structure was the king who had the power to enact laws. Kautilya advises the King to promulgate dharma when the social order based on the Varnas and Ashramas (stages in life) perishes.
There were 27 superintendents (Adhyakshas) appointed by the Muaryan Empire to regulate economic activities of the state. This included trade and commerce, agriculture, weights and measures, mining, weaving and spinning.
In the 4th century B.C., Nanda kings ruled Magadha dynasty and this dynasty was the most powerful kingdom of the north. A Brahman minister called Chanakya also known as Kautilya/ Vishnupgupta, trained a young man, Chandragupta from the Mauryan family. Chandragupta organized his own army and overthrew the Nanda king in 322 B.C.
Ashoka was the son of Bindusara. He was governor of Taxila and Ujjain during his father’s reign. Ashoka sat on the throne around 268 B.C after successfully defeating his brothers. There was an interval of four years between Ashoka’s accession to the throne (273 B.C.) and his actual coronation (268 B.C.). Therefore, it appears from the available evidence that there was a struggle for the throne after Bindusara’s death.