Has this experiment been repeated since? On kids who weren't growing up in the near aftermath of a great war?

Would you argue that there is some attribute that is fundamentally different between children growing up in the post WWII era and today (or any other era for that matter)? My very anecdotal evidence is that once any sort of division into groups occurs, children act in a matter very similar to the Ratters and Eagles. There was a gifted and talented program at my elementary school, which consisted of students from across the county who were bussed into the school and took classes seperately from other students. At the graduation pool party, an innocent slash contest escalated into a full out fight between over.. I'd say approximately 40 students, some of whom inflicted relatively significant injuries. Of course, in group bias had always existed throughout the school years, but violence associated with in group bias isn't something that I feel would be atypical in children of different eras.

Um ... all of human history? Does that count?