Final answer:
The three main trends in defining markets in recent decades are electronic commerce, increased competition due to globalization, and improved relationship management facilitated by improvements in technology and international trade agreements.
Step-by-step explanation:
The three trends mentioned in your answer are: electronic commerce, increasing competition and globalization, and relationship management. These trends reflect the shifts in market definition due to technological advances and the global spread of products and services. Globalization has progressed for reasons such as lowered transportation costs, advancements in computing and telecommunications, and international trade agreements, which facilitate easier and cheaper long-distance economic activities.
Electronic commerce allows consumers to purchase items from all over the world, thereby increasing competition among local retailers. Moreover, business-to-business websites enhance the interaction between buyers and suppliers globally, intensifying competition in the business supplies market.