Final answer:
The option 'external environment' (C) is not one of the competitive forces as per Michael Porter's Five Forces model. This model outlines suppliers, customers, new entrants, substitutes, and competitive rivalry as the key forces.
Step-by-step explanation:
The question asks to identify which option is not one of the competitive forces. According to Michael Porter's Five Forces model, which is widely used in the field of buasiness strategy and analysis, competitive forces include the threat of new entrants, threat of substitute products or services, bargaining power of customers, bargaining power of suppliers, and the intensity of competitive rivalry. From the options given in the question, external environment (C) is not directly one of Porter's competitive forces. While the external environment certainly affects a firm's competitive strategy, it is not counted among the internal industry forces identified by Porter's model.
Likewise, other competitors (B) are an essential part of the competitive rivalry force, one of Porter's Five Forces. Suppliers (A) and customers (D) are also part of this model as they hold the bargaining power, which affects a business's profits significantly. If there is strong competition within an industry, such as the technology sector or the airline industry, the competitive pressure and strategies employed are stark examples of Porter's forces at work.