Barriers to entry primarily protect existing firms from which of Porter's 5 forces?

Barriers to entry predominantly serve to protect existing firms from the threat of new competitors. When high barriers exist—such as significant capital requirements, strict regulatory policies, established brand loyalty, or economies of scale—new entrants may find it difficult or unfeasible to enter the market. This limitation allows current companies to maintain their market share and profitability without the immediate risk of new competitors undercutting prices or eroding their customer base.

In contrast, the other forces in Porter's framework deal with different aspects of competitive dynamics. For instance, the bargaining power of suppliers and buyers relates to the ability of these stakeholders to influence prices and terms. The threat of substitute products concerns alternatives that can fulfill the same customer need, but these factors are less directly influenced by the capabilities to enter the market. Therefore, strong barriers to entry serve mainly to mitigate the risk posed by potential new competitors.