Third-party marketplaces concentrate most of the world's online shopping, and the model keeps expanding: social platforms now run marketplaces, US retailers are opening their marketplaces to international shoppers, and Latin America has become the most contested battleground. This FAQ covers how marketplace power is distributed, where the growth is, and what sellers should do about it in 2026.

The news: Amazon will bring inventory from Roku to its demand-side platform (DSP), the two announced at Cannes Lions, starting in Q4 2025. Our take: Amazon’s Roku partnership is a well-timed announcement to convince advertisers to stick with their CTV ecosystems even amid tightening budgets.