I don't remember ever seeing "internecine" without its journalistic tagalong "warfare".
Johnson was not taken to task for this error. On the contrary, his dictionary was so popular and considered so authoritative that this error became widely adopted as correct usage. The error was further compounded when internecine acquired the sense “relating to internal struggle.”
That's an interesting note in the link you provided, Sitran. Thus mutually destructive antagonism within the city (or school) could more properly be "intra
necine" and aggression with clear outsiders as "extra
necine". Unless one group really, really wanted the others eliminated at all costs, which becomes a teen video game or "reality" program along the lines of "Xtreme