Machiavelli mentions Pisa at the end of the passage "to prove that cities that are not destroyed will eventually rebel".
Explanation:
The chapter 5 of “The Prince” summarizes the central ideas that are adapted to freedom, destruction, occupation, or establishment of an oligarchy—and says that destruction or construction is best.
Machiavelli uses compare and contrast text structure in this excerpt. The text structure shows how the prince can fail. This helps the author to convey his central idea.
The author mentions Pisa at the end of the passage to show that the non-destroyed cities will join the rebel.