In some ways this seems to resemble the problematic of "real abstraction" in Marx. In the same way that the abstraction of labor isn't simply produced by thinking and speaking, the comparability of different things (nation-states, cultures, etc.) does not always originate in the brains of crazy social scientists (nor does it spring from the essence of humanity in general).
Marx has something interesting to say about comparison on p. 149...
The relative value-form of a commodity, the linen for example, expresses its value-existence as something wholly different from its substance and properties, as the quality of being comparable with a coat for example; this expression itself therefore indicates that it conceals a social relation. With the equivalent form the reverse is true. The equivalent form consists precisely in this, that the material commodity itself, the coat for instance, expresses value just as it is in its everyday life, and is therefore endowed with the form of value by nature itself. Admittedly, this holds good only within the value-relation, in which the commodity linen is related to the commodity coat as its equivalent. However, the properties of a thing do not arise from its relations to other things, they are, on the contrary, merely activated by such relations.
Hmm... comparability on the one hand, everydayness on the other. Not an easy passage to unpack! It suggests a few questions to me on the subject of comparative history. How do we get from the nation-state-form to the commodity-form (or vice-versa)? Are "real" comparisons a sort of one-way street?