Interesting snippet from the newly-published notes of conversations between Adorno and Horkheimer in 1956, when they were attempting to write an updated version of the Communist Manifesto. (I should stress that I’ve so far seen only the extract published online at http://www.the-utopian.org/post/12034084404/towards-a-new-manifesto, not the whole thing, published last month by Verso).
Horkheimer: I believe that Europe and America are probably the best civilizations that history has produced up to now as far as prosperity and justice are concerned. The key point now is to ensure the preservation of these gains. That can be achieved only if we remain ruthlessly critical of this civilization.
Adorno: We cannot call for the defence of the Western world.
Horkheimer: We cannot do so because that would destroy it. If we were to defend the Russians, that’s like regarding the invading Teutonic hordes as morally superior to the [Roman] slave economy.
The analogy seems to have two facets: firstly, a historical one, emphasising the problem that a genuine and vital civilisation may rest on an immoral and inhuman base (the West depends on capitalism as Rome depended on slavery); secondly, a historiographical one, emphasising the dubious antecedents of any celebration of barbarians smashing civilisation (given that this was a prominent theme in early-mid C20 German accounts of the end of Rome). Of course, the fact that the old image of invading hordes has now been abandoned by historians allows us to sidestep the wider political issues…
Sphinx 
Exactly what model of historiography Horkheimer is espousing is unclear, to me, especially as he later makes this measured and tranquil comment: “The world is mad and will remain so. When it comes down to it, I find it easy to believe that the whole of world history is just a fly caught in the flames.” So what should historiography be, then?
In any event, what is curious in this snippet is that Horkheimer goes on to say, “We have nothing in common with Russian bureaucrats. But they stand for a greater right as opposed to Western culture.” So it is not only that the West and Rome are “genuine and vital” while resting on an immoral base, but that they “stand for” that immoral base, while those who “stand for a greater right” remind Horkheimer of Cesare Borgia.
Perhaps it is this convolution that leads Horkheimer to call world history “a fly caught in the flames?”