Which of the war had changed the thinking of King Ashoka towards War?

War with Kalinga

During the eighth year of King Devanampiya Piyadassi's reign, he led a military campaign and conquered the country of Kalingas, located in present-day coastal Orissa. The war resulted in the deportation of one hundred and fifty thousand people, the death of a hundred thousand, and the loss of many more lives. Witnessing the devastating consequences of this conquest, King Devanampiya underwent a profound change of heart. Subsequently, he dedicated himself to the study, love, and promotion of Dhamma (Buddhist teachings). He actively engaged in instructing the people in the path of Dhamma.