Answer: In this context, the dictionary definition of the word internecine is mutually destructive.
Explanation:
The adjective internecine is often used in context of warfare or conflict. In this case, this word stresses the fact that both sides (the Red Republicans and Black imperialists) were engaged in this conflict which caused only harm and no good for either of the sides. This adjective is used to refer to a group of people which are fighting each other in vain - there are no winners, and no benefit.
