C. He was horrified at the brutality of war when conquering the region of Kalinga
Emperor Ashoka's conversion to Buddhism is largely attributed to the profound impact the violent aftermath of the Kalinga War had on him. The immense suffering and loss of life caused by the war led him to seek a path of peace and non-violence, which he found in Buddhism. This transformation guided his subsequent policies and efforts to promote the principles of Buddhism throughout his empire.