Machiavelli writes, at the beginning of chapter 1, that "All states...have been and are either republics or principalities." As the title suggests, almost all of The Prince is devoted to analysis of principalities, which Machiavelli divides into two categories: hereditary and new. (He discusses republics in detail in other works.)
Principalities are ruled by monarchs, or "princes." New principalities include states established by a leader who becomes a prince as well as those formerly independent territories that have been annexed and added to an existing principality. They also include large kingdoms, like France in particular, though the focus of The Prince is the smaller principalities in Italy. One other category of principality not mentioned at the beginning of the book (but discussed later) is what Machiavelli calls "ecclesiastical principalities." These states owe their power to the "ancient ordinances of religion" and include the lands held by the Catholic Church.
It's important to recognize that Machiavelli lived through a time of political upheaval, as Italy was ravaged by the experience of the Italian Wars. This context certainly played a role in influencing The Prince, which advocates for political opportunism and ruthlessness on the part of would-be princes and largely views political success in terms of one's capacity to hold and wield power.
Machiavelli's view of statecraft is largely shaped by a sense of contingency. He sees politics as inherently unpredictable, with chance playing a key role in shaping political outcomes. Reversals can occur at any time, and they are not entirely under the power of would-be princes. This is critical in shaping his ruthless perception of statecraft. If people cannot know with any reliability what the future might bring, rulers must be extremely energetic in how they respond to any oncoming crisis or in how they seize those opportunities which might arise.
In The Prince, Machiavelli describes authoritarian regimes maintained by coercion, force, brutality, deceit, and so on. Machiavelli describes these regimes as "principalities" which are, according to Machiavelli, in contrast to states based upon the principles of a republic. Machiavelli describes in detail how a ruler should maintain power though spreading fear and using strong military force to subdue subjects and quash any chances of rebellion.
Machiavelli describes a good ruler as one who is willing to use of force and violence against citizens but also knows how to use the mere existence of the regime as a means to ensure subservience. Essentially, Machiavelli describes an authoritarian regime that employs either the direct use of violence or the unspoken threat of violence to maintain power.
Machiavelli was a product of his times. Italy in the 15th and early 16th Centuries was an extremely turbulent system of city-states riven by violence and intrigue. In addition to the governments of each city-state, the Catholic Church fought to extend its influence, and foreign incursions from countries like Spain and France further destabilized the region. Most importantly, Machiavelli observed the rule of the notorious Borgia family, the patriarch of which was Pope Alexander VI. The reign of the Borgias was bloody and provided Machiavelli insights into the way governments conducted themselves and what measures were adopted to maintain power while holding territory together. His positions of military and political importance enabled him to have a front row seat to some of the most instructive and disreputable political practices of the day.
In short, the kinds of states Machiavelli describes are autocratic regimes that resorted to any level of brutality to maintain power. The lessons he learned from his experiences and observations provided the basis of his widely known study, "The Prince." The theme of that study is that rulers had to be willing to employ violence judiciously and to maintain a presence throughout the breadth of their territory. They had to be cautious about going too far in the use of violence, but that it was an inherent component of governing. Machiavelli also emphasized the importance of care in how a ruler surrounded himself with advisers, as ensuring continuing loyalty was vitally important for self-preservation and for the survival of the state.