It was from The Prince that Machiavelli gave his grievance. His issue was clearly with the various condottieri that dominated Italian battlefields; he spent a whole chapter on it condemning them. He had good reason too considering how many of the most powerful Italians of his time were just plain mercenary captains at some points in their lives.

He also condemned the use of "auxiliaries" (in this case to put simply is just using soldiers from another state to fight one's own wars) but that's not in the topic.

It's the alternative that he proposed that led to my question, however. He did not make clear what he think is "one's own forces" until the end where he said that it's either "subjects, citizens, or dependents." Citizens are clear enough; Machiavelli was probably referring to things from a polis' militia to the Roman Republic's armies. On subjects and dependents these are not so clear. He could mean a full-time professional fighting force or he could mean a feudal levy. If it is the former then one can conclude he recognized the distinction between them long before the French Revolution and the era of national armies that began with, whatwasit, the levée en masse.

Of course, prior to him and much later I agree things were never clear. After all the Varangians, mercenaries by their very definition, proved to be the most loyal of all Byzantine fighting forces when all hell breaks loose.