Complex sentence: His father set him up as a prince with territory carved from the Papal States, but after his father's death he was unable to retain power for long, according to Machiavelli this was due to his planning for all possibilities but his own illness.
Split into simpler sentences: His father set him up as a prince with territory carved from the Papal States, but after his father's death he was unable to retain power for long. According to Machiavelli this was due to his planning for all possibilities but his own illness.