Pope Boniface VIII was Dante Alighieri’s worst enemy.
First, the Pope betrayed Dante’s beloved White Guelphs party. The party was originally the Guelphs who split into two parties, The White Guelphs and the Black Guelphs, after defeating the Ghibellines in the Guelph-Ghibelline conflict. The split originally occurred along familial lines, but later the split was prominent in the ideological differences based on opposite views on the papal rule in Florence- which was were the two parties resided. The Blacks supported the Pope and the Whites wanted more freedom from Rome.
Initially the Whites were in power, so they expelled the Blacks. In response, Pope Boniface VIII planned a military occupation of Florence. In 1303, Charles of Valois, who was the brother of King Philip IV of France, was to visit Florence because he was appointed peacemaker by the Pope. It was believed that Charles of Valois had received other unofficial instructions, so the council sent a delegation to Rome to ascertain the Pope's intentions. Dante was one of the delegates.
Pope Boniface quickly dismissed the other delegates and asked Dante alone to remain in Rome. At the same time, Charles of Valois entered Florence with the Black Guelphs, who in the next six days destroyed much of the city and killed many of their enemies. A new Black Guelph government was installed and Cante de' Gabrielli da Gubbio was appointed podestà of the city.
Secondly, Dante was condemned to exile for two years and ordered to pay a large fine. He did not pay the fine in part because he believed he was not guilty and in part because all his assets in Florence had been seized by the Black Guelphs. He was condemned to perpetual exile, and if he returned to Florence without paying the fine, he could be burned at