Only because ideological states tend to deteriorate faster than the nation-state does. You're right though that nation-states have made wars larger and uglier than they have been, though that in itself is cyclical. War was tame after the Thirty Year's War, ugly again during the Napoleonic/US Civil War phase, tame again in the interim, the World Wars providing enough examples of atrocities that guys like Sauron look like pikers, tame again thereafter.