A stray thought provoked by a stray observation. I picked up Modris Eksteins' Rites of Spring, a history of European culture from 1914-1945, about the changes produced by the Great War, and quite by chance opened to this paragraph:
If the war was reduced, certainly by 1916, to reflex responses, then the assumptions of the civilizations and cultures fighting the war were all-important. And here the crucial catchword for those assumptions was "duty" or devoir or Pflicht. After the gloss of heroism had worn off in the first month of the war, and as the war settled into the enervating phase of attrition, the concept of duty became the linchpin to the effort. As long as the word retained any semblance of meaning, spoken or unspoken, the war would continue. As long as soldiers could somehow relate their reflexes and instinctive behavior in moments of reflection to an underlying sense of responsibility, they would continue to fight, despite horror, weariness, and even despondency.Of course it follows from this that, if "duty" had come to be thought of as meaningless, then the war would have ceased--which would have been a very good thing.
I note this because I think that the wars of the 20th c. have much to with why "duty" is not taken seriously in Europe and the U.S. (although one might speculate that the U.S. did not have anything like the reaction of Europe until Vietnam)--not that these considerations touch Cicero's discussion, in principle, since on his theory of a just war it is clear that the Great War would not have been just and thus not a field of "duty".