Machiavelli wasn't just "worried"; he'd seen it be attempted (sometimes successfully). Facino Cane, Vitellozzo Vitelli, and famously Francesco Sforza. (Often this would happen on the death of the previous hereditary ruler, or through taking independent control of territories conquered in an employer's name.)

https://en.wikipedia.org/wiki/Facino_Cane

https://en.wikipedia.org/wiki/Vitellozzo_Vitelli

https://en.wikipedia.org/wiki/Francesco_I_Sforza