Question

why did Ashoka give up Fighting and become a propagator of this

Answer 1

After the Kalinga war, Ashoka saw that many people were killed and some were injured and because of the fight , their families also suffered then he realised that he had attain nothing then he gave up fighting and became the devotee of Gautam Buddha

Answer 2

after the kalinga war he was influenced by seeing the circumstances there and thus decided giving up war and thus became a saint