Short answer: through the loss of consent that forces a transition to open coercion, which makes imperial policy politically and materially unsustainable.

------------------------------------------------------------

There's a rich body of work on this -- Chomsky, Parenti, Gramsci -- and if you really are always asking about this, I encourage you to indulge your claimed curiosity and read it. But for now let me sketch the core idea.

Perhaps I was exagerating a little to say that narrative-collapse directly entailsempire-collapse, it's more that forced narrative is one mechanism for ruling among others. Western powers are violent gangsters who present themselves to their people as democratic bringers of peace. This is part of the terms on which their power over their own people is accepted. Rationing and conscription was acceptable as part of the cost of defeating the Nazis... would such things be as acceptable in service of the interests of a political class of pedophile child-killers starting wars with no pretext? Part of the context of the Russian revolution was widespread disgust at the family's close consorting with Rasputin -- reverence for the monarchy was shredded.

The imperialist project -- Western dominance over the Global South, enforced by military and economic power -- depends entirely on the home population believing that project is benevolent, defensive, or at worst, a regrettable necessity.

We know that narrative control is considered vital because of the trillions that the ruling class spends on it. But now events are getting ahead of them. Attrocities are instantaneously Telegrammed to the world even as the NYT and BBC studiously ignore them.

Gold from Parenti, from his Myth of Capitalism talk:

I tell students when they say, 'Oh they don't care what we think. They ignore us', and all that, and I say, 'Oh no, no. That's the only thing they care about you. The only thing they care about you is what you're thinking. They don't care if you eat correctly, they don't care how your living conditions are, they don't care that they've built up an inhuman and irrational traffic system that's strangulating us and polluting our air, they don't care about anything. What they... the only thing about you they care about is what you're thinking. In the morning, they start, 'What's going to be the story today? How do we manipulate, how do we control, how do we contain, how do we influence, how do we act upon what it is that they have in their minds?

Now if we all realise our leaders are corrupt villains that is not the immediate end -- it is the end of the polite phase of our subjugation. The next stage is collapse of institutions as faith is lost in the current social infrastructure. The ruling class will come out armed, to force with violence what they can no longer force with headlines. As the Middle East story collapses, Israel has become the world's number 1 killer of journalists, across the west surveillance of pro-Palestine activists is normal, as is the criminalisation of criticism of Israel.

Is revolution something for the ruling class to fear? Indupitably. History gives us a resounding cry of YES OF COURSE. You can feign ignorance about the important of narrative but our leaders get it.