Final answer:
The element that is not necessary for conflict to exist is 'D) Common interests'. Conflicts usually arise from incompatible goals, interference, and an expressed struggle, not from shared interests.
Step-by-step explanation:
Based on the text's definition, all of the following elements are necessary for conflict to exist EXCEPT: D) Common interests. In context, conflict arises when there are perceived incompatible goals (A), when one or more parties interfere with each other's goals (B), and when there is an expression of struggle (C). Common interests do not necessarily generate conflict; in fact, they often help alleviate it, as they represent a unifying factor that can help involved parties find a resolution. An element like common political culture (c from the provided options), would fall under common interests which suggests a harmony rather than a cause for conflict.