Abstract: In the digital era, e-commerce platforms have transcended the traditional role of retailers by implementing backward integration strategies, thereby assuming the dual roles of channel service providers and product competitors. This transformation has given rise to increasingly complex relationships characterized by the simultaneous coexistence of competition and cooperation between upstream and downstream supply chain members. However, existing studies have yet to provide a systematic understanding of the structural characteristics and evolutionary mechanisms underlying such coopetitive relationships. Against this backdrop, this study investigates the drivers and consequences of e-commerce platforms’ backward integration strategies, with a particular focus on the formation and evolution of coopetition between e-commerce platforms and upstream manufacturers under multiple channel configurations. To this end, we develop a supply chain model consisting of one e-commerce platform and two quality-differentiated manufacturers. We identify four decentralized channel structures without backward integration (NI1, NI2, NI3, and NI4), formed through different configurations of the reselling and marketplace modes, as well as four integrated channel structures with backward integration (IH1, IH2, IL1, and IL2). Building upon this framework, we analyze the platform’s backward integration decisions and the resulting multi-agent coopetitive interactions across alternative channel structures. Furthermore, we examine how integration cost (z), the degree of product quality differentiation (θ), and the relative production-and-sales efficiency (k) affect the profitability of backward integration strategies. Numerical simulations are then conducted to derive the conditions under which backward integration becomes the platform’s dominant strategic choice. The results reveal that backward integration can effectively mitigate the double marginalization problem within the supply chain while strengthening the platform’s channel leadership and bargaining power. In the private-label scenario characterized by zero integration cost, the platform prefers to integrate the high-quality manufacturer when the low-quality product exhibits relatively low production-and-sales efficiency. As the relative efficiency of the low-quality product increases, however, the platform’s optimal strategy shifts from integrating the high-quality manufacturer to integrating the low-quality manufacturer. By contrast, in the self-production scenario involving positive integration costs, the impact of the low-quality product’s relative efficiency on the platform’s integration decision is exactly the opposite of that observed in the private-label setting. Moreover, backward integration generates asymmetric external effects: while it enhances consumer surplus and overall social welfare, it simultaneously places the non-integrated manufacturer in a disadvantaged position characterized by both market-share erosion and weakened bargaining power. This study contributes to the literature by providing a theoretical foundation for understanding how e-commerce platforms employ backward integration strategies to improve supply chain coordination and operational efficiency. It also offers new insights into the formation and evolution of complex coopetitive relationships within supply chains in the platform economy.

Key words: E-commerce platform, Backward integration, Channel structures, Vertical differentiation, Coopetition game