The central idea is that the white people are worse than natives insofar that it may seem like the Natives are brutal savages, but it is actually the colonists who are worse because they "poison the heart" while the natives only "scalp". He explains that he tried and failed and is sorry that soon the Natives will be just like the White men. Expand this into two paragraphs and add a bit more quotes.
Answer:
One reason why this is believable is because di Coppo Di Stefano Buonaiuti was in Florence at the time when the Black Death hit Florence in 1338. One reason why this passage isn't believable is because he was only two when it happened so might not remember it all.
Probably the kingdom of axum