The Ruling Class by Gaetano Mosca — originally published in Italian in 1895 — is an attempt to understand ruling classes:
how they function,
how they stay in power;
how they fall from power;
and so on.
Of course, all societies have "a class that rules and a class that is ruled." Moreover, the ruling class is a minority, ruling over a majority: it must be so. Typically the ruling class is headed by a single individual. It is the rest of the ruling class that enforces respect for him and his orders.
Ruling classes always invent a moral or legal basis for their power. Mosca calls this a political formula. The ruler might be a king that rules as God's Anointed, or he might be a US president that rules by the will of the people. There is always a "political formula."
Vital to every society are the social mechanisms (e.g., "respect for law, government by law") that regulate the disciplining of the "moral sense," institutions like religion and government that institutionalize respect and obedience for law and government. Mosca calls this "juridical defense."
What makes or breaks a ruling class? Mosca believes that it is the "intermediate strata" in the ruling class that make or break it. Moreover the success of heads of state often depends on their success in "timely reforms of the ruling class."
Thus, for Mosca, the real achievement of heads of state is "their success in transforming ruling classes by improving the methods by which they were recruited and by perfecting their organization."
And the fundamental challenge is to eliminate or reduce "those great catastrophes" that thrust people "back into barbarism." Nations die when their ruling classes are incapable of reorganizing in such a way as to meet the needs of changing times.
And that requires a ruling class that attempts "to see a little beyond its immediate interest."