Final answer:
The most profound change for firms in global marketing is treating the world as one integrated market, a shift driven by technological and globalization trends that increase competition and connectivity across borders.
Step-by-step explanation:
The most profound change for firms at the global marketing stage of internationalization is D. Companies treat the world, along with the home market, as one market. This approach is driven by the interconnected shifts of technology and globalization, which have enabled a significant improvement in communications technologies. Consequently, this facilitates business-to-business interactions and consumer purchasing across national borders, enhancing competition and necessitating an integrated global marketing strategy. This scenario highlights the need for firms to recognize the global market as a unified entity, rather than merely focusing on temporary surpluses or individual foreign market opportunities.