Final answer:
The threat of substitutes, specifically digital photography, proved to be the strongest force according to Porter's Five Forces model in the competition between Kodak and Fuji in the photographic film industry.
Step-by-step explanation:
In the context of the photographic film industry, particularly the competition between Kodak and Fuji, Porter's Five Forces model helps to assess the competitive intensity and therefore the attractiveness of an industry.
The force that ultimately proved to be stronger and more disruptive was B) Threat of substitutes.
The rise of digital photography, which is not a direct competitor in the traditional sense but rather a technological substitute, had a monumental impact on the industry.
The digital revolution greatly diminished the market power of both Kodak and Fuji, as it rendered traditional photographic film largely obsolete.
Evidence of competition on the basis of price, advertising, and product differences did exist, yet the threat of substitutes in the form of digital technology was the decisive factor that reshaped the industry, making it extremely difficult for firms relying on traditional film to adapt and survive.