5 ideas
A ruling class holds power less through force than by getting its own interests accepted as common sense, so that subordinate groups treat the existing order as natural and give it their active consent. Gramsci's formula is that the state equals political society plus civil society: hegemony protected by the armor of coercion, with force held in reserve for the moments when consent fails.
In Tsarist Russia the state was everything and civil society was weak, so a frontal assault (war of maneuver) could seize power. In the West, civil society (churches, schools, press, parties, unions) forms a dense system of trenches behind the state, so taking the state alone does not win. Revolution there requires a slow war of position that wins cultural and moral leadership inside those institutions before political power is taken.
Every social group that rises to power creates its own organic intellectuals: organizers, technicians and ideologues who give it coherence and awareness of its own function, as the capitalist entrepreneur brings forth the economist and the manager. Traditional intellectuals such as clergy and academics present themselves as autonomous and classless, but they are residues of earlier class formations. A group's bid for hegemony depends on producing its own organic intellectuals and on absorbing the traditional ones.
Gramsci reads Italian unification (1860s) as a passive revolution. Cavour's Moderates, a coalition of northern industrialists and southern landowners, united Italy from above, while Mazzini's Action Party failed to mobilize the peasantry with land reform and was absorbed piece by piece through trasformismo. The outcome was a new state lacking mass consent and a subordinated South, a structural weakness Gramsci links to the later rise of Fascism.
A crisis of authority occurs when the ruling class loses consent and becomes merely dominant, ruling by coercion alone, because the masses have detached from traditional ideologies and parties. In that interregnum, when the old is dying and the new cannot be born, a great variety of morbid symptoms appear.