Final answer:
Ashoka's attack on Kalinga prompted a period of introspection and development of policies focused on welfare and morality. Hence, the correct answer is option D.
Step-by-step explanation:
Ashoka's attack and conquest of Kalinga in 261 BC had a significant impact on his rule. The event caused Ashoka to have a period of introspection and development of policies focused on welfare and morality. Prompted by the intense human distress caused by the war, Ashoka embraced non-violence as the creed of his life, adopted Buddhism as his personal religion, and implemented reforms to improve the lives of his subjects.
This transformation is evident in his Edicts, where he expresses remorse for the suffering caused by the war and emphasizes moral principles and social welfare in his rule.