Read this paragraph from chapter 5 of The Prince.

There are, for example, the Spartans and the Romans. The Spartans held Athens and Thebes, establishing there an oligarchy: nevertheless they lost them. The Romans, in order to hold Capua, Carthage, and Numantia, dismantled them, and did not lose them. They wished to hold Greece as the Spartans held it, making it free and permitting its laws, and did not succeed. So to hold it they were compelled to dismantle many cities in the country, for in truth there is no safe way to retain them otherwise than by ruining them. And he who becomes master of a city accustomed to freedom and does not destroy it, may expect to be destroyed by it, for in rebellion it has always the watchword of liberty and its ancient privileges as a rallying point, which neither time nor benefits will ever cause it to forget. And whatever you may do or provide against, they never forget that name or their privileges unless they are disunited or dispersed, but at every chance they immediately rally to them, as Pisa after the hundred years she had been held in bondage by the Florentines.

What idea is stressed in the passage