Ashoka  was succeeded by weak rulers. This encouraged the provinces to proclaim their  independence. The arduous task of administering such a vast empire could not be executed by the weak rulers. The mutual quarrel among the successors also contributed to the decline of the Mauryan empire.

Religious causes:- 

 Ashoka had invoked a strong religious doctrine based on the law of piety. The policy of peace during the rule of  Ashoka was mainly due to his influence over the vast empire. The Brahmanas who before the Mauryas had contributed to the establishment of the Mauryan rule now  organised to the establishment of the old order. This quelled the impact of the Buddhist doctrine which was made a political, economic and social policy besides influencing the cultural sphere of the life during the Ashokan period.

The inactive army who's officers were made Dharmamahamantras for propagating the law of piety, lost their skill to defend themselves.