History
Michels stressed several factors that underlie the "Iron Law of Oligarchy." Darcy K. Leach summarized them briefly as: "Bureaucracy happens. If bureaucracy happens, power rises. Power corrupts."

The reasons
The "iron law of oligarchy" states that all forms of organization, regardless of how democratic or autocratic they may be at the start, will eventually and inevitably develop oligarchic tendencies, thus making true democracy practically and theoretically impossible, especially in large groups and complex organizations. The relative structural fluidity in a small-scale democracy succumbs to "social viscosity" in a large-scale organization. According to the "iron law," democracy and large-scale organization are incompatible.

The consequences
An example that Michels used in his book was Germany's Social Democratic Party.

Criticism

Robert Michels und das eherne Gesetz der Oligarchie by Gustav Wagner in "Wer wählt, hat seine Stimme abgegeben" Graswurzel Revolution pp. 28