The text is a primary source and gives a cursory information of what happened wit Ashoka and Kalinga.
Step-by-step explanation:
1 Any primary source is one that has come down to us intact and Ashoka's edicts are one of the few that have.
This edict says that Ashoka was remorseful about the death of many people in Kalinga when he conquered that country.
2 This and many other secondary sources have suggested that this indeed was a terrible war and Ashoka did win it , but at a terrible cost of men from his side and a complete slaughter of the natives.
3 This incident had him change his mind about warfare and he would eventually take up Buddhism too.