Machiavelli, following more ancient political theorists, claims that there are, generally speaking, three types of government: kingdoms or principalities, aristocracies, and democracies. He points out, though, that it is more accurate to say that there are six, since each type has its own defective counterpart. Through a process of degeneration and decay, kingdoms become tyrannies, aristocracies become oligarchies, and democracies become anarchic ochlocracies.
The first ruler or prince comes about when smaller groups and clans place a leader, presumably the strongest among them, at their head in order to establish organization, protection, and law. In return, this leader is given obedience and, from this relationship, civil justice is born. Assuming that this dynamic persists, the next ruler chosen will not necessarily be the most powerful in the sense of being the strongest; he will, however, be the most able at maintaining justice among his people. It is here that Machiavelli says the process of degeneration may begin. Rulers, instead of being chosen for their ability, or even chosen at all, come to power through hereditary succession. Because of this, the rulers lose all necessary virtue, excelling only in the pursuit of power and pleasure. As a result of this abdication of concern for the common good, these new leaders are eventually despised by the people over which they rule. Living in fear of the people, these princes are more likely to enact violent deeds and become tyrannical rather than seek to assuage the displeasure of the citizenry.
At this stage, Machiavelli says that the tyrant begins to face opposition from men of wealth, power, nobility, etc. Upon the elimination of tyrannical rule, the mass of people fall under the rule of this small elite. These men, only just ridding themselves of the political yoke of tyranny, desire to keep the favor the people. They therefore take care to execute government effectively and also scrupulously observe the law themselves. However, just as the rule of a single virtuous man cannot endure perpetually, so too the virtuous collective must pass their rule to a group which lacks the necessary virtues. As the king becomes the tyrant, so too the aristocrats become oligarchs. Now, instead of turning to another small elite, the masses lend their support to any who are willing to destroy the oligarchs. Exhausting the rule of the one and the rule of the few, the people turn to the rule of the many.
Machiavelli, like Socrates in Plato's Republic, is particularly harsh toward democracy. He argues that democracies, like all other types of political organizations, can indeed maintain themselves at first. But unlike other forms of government, he does not think that a democracy can even outlast the generation which establishes it. Democracies immediately become anarchical, with each individual following only his own passions. Anarchy, though, is untenable. It must give way to either monarchy or monarchical tyranny, that is, if the state has not already been conquered by its more powerful and stable neighbors.
Notice, the distinction between a virtuous government and its opposite is whether the state's rulers are concerned with the common good or their own personal good. This contrast is most visible in democracy, where the concern for the common good is almost completely lost. Each man becomes a ruler to himself, it is a land of little tyrants. In our democratic regime, the very notion of the common good is rejected.