Internecine

Adjective

1. Mutually destructive; most often applied to warfare.

   "Internecine strife in Gaza claimed its most senior victim yesterday when militants assassinated one of the most hated security chiefs there."

2. Characterized by struggle within a group, usually applied to an ethnic or familial relationship.

   "The Mongol people were plagued by internecine conflict until Genghis Khan unified them by focusing their aggression outwards on other peoples."