Bertram correctly reports that Ripstein uses the notion of "barbarism" to address the "problem" posed by Kant's remarks on revolution in the Doctrine of Right. The problem is described in Ripstein's telling in terms of the difficulty that some states (notoriously, that of the Nazis) are such that they surely are no advance on the state of nature. Ripstein uses the notion of "barbarism" to characterize these states and, in so doing, to legitimate rebellion against them where rebellion now becomes characterized as "the creation of a state where there was none before" (Ripstein, 338).
There are certainly problems thinking about what Kant says about revolution and the way Ripstein tries to deal with it. Bertram's response is somewhat tiresome, however, since it reiterates a kind of sniggering, "oh, look, Kant has some bad arguments" form which I have discussed previously. This really is no kind of response to any philosopher. Bertram mentions, in his posting, how reading Ripstein made him prefer Rousseau, Marx and Hegel, above all for their attention to "anthropology". However, the number of "bad arguments" that one can find in each of these three, not least in their anthropology, are legion. So it might be better not to start a war of "who has the worst arguments".
Bertram also makes another error in his response to Ripstein when he insists on a set of responses that will transcend the "example" (if they can be termed that!) of the Nazis, insisting that, if the notion of "barbarism" is of any use it should also be able to guide our political responses to Franco's Spain and Israel. To suggest that the distinction, just as such, is sufficient to deal with such complex empirical situations is no more helpful than the view that Rousseau's accounts of where a republic exists and where it does not should so easily be applied. The other case given, however, that of the US when it had slavery is rather simpler since, as Ripstein states explicitly: "A condition in which some are not allowed to have anything as their own, or in which they are enslaved or murdered by others, is not a difficult case" (342). In such cases there is not a state of right since the state of right explicitly requires equal rights to freedom. So if there not such rights then, for everyone in such a condition, there is not an advance on the state of nature. This is precisely the point of Ripstein's invocation of the notion of "barbarism".
The point behind these objections to Kant seems, however, to be pointed up more by Bertram's demand for an anthropology that he rightly finds missing in the Doctrine of Right. As some have pointed out in response to Bertram's posting there is plenty of anthropological reflection by Kant if that is what you prefer (though there are good reasons not to prefer it, at least not as it is simply given). The Doctrine of Right is meant to provide a "strict" account of an a priori view of right though it requires supplementing by further "principles of application". There are good reasons for thinking this further supplementation is not well carried out by Ripstein and I have many reasons for disagreeing with Bertram that a "better book" on Kant's philosophy of right is unlikely to be written. Having said which, it would be good to see debate that centred not always on "examples" and "cases" but concerned itself rather more with principles, laws, rules and the generic basis of Kant's view.