The sequence that best explains the events that led to the spread of Buddhism during Asoka's reign is:
Asoka rose to power through civil war. Asoka took over Kalinga by force. Asoka adopted Buddhism. Asoka became a just and compassionate ruler.
This order highlights the initial rise to power, the violent conquest of Kalinga that profoundly affected Asoka, his subsequent adoption of Buddhism, and his transformation into a compassionate ruler dedicated to spreading Buddhist principles.