It can spread either in a directed fashion (retaliating against the perpetrators) or in a generalized fashion (harming nondisputants nearby). Either way, however, a single murder can set off a cascade of killings. Acts of aggression typically diffuse outward from a starting point — like a bar fight when one man swings at another who ducks, resulting in a third man getting hit, and soon (in what has become a cliche precisely because it evokes deep-seated notions of unleashed aggression) punches are flying everywhere.
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