A six-part walkthrough of the U.S. e-commerce marketplace landscape for 2026 — five chapters covering Amazon's dominance, eBay's intentional niche, the contested $15–22B mid-tier band, Shopify's decentralized model, and the vertical specialists — followed by the underlying GMV data table that ties it all together.
1. Amazon's Absolute Command
Amazon 3P sales hit ~$300B — over 7× nearest competitor (eBay $39B). Rufus AI added $12B incremental sales (2025). Amazon Haul (sub-$10 storefront) ~$2B.
2. eBay's Intentional Ceiling
eBay holds at $39B GMV — stable niche play. Strategic shift to enthusiast categories (cameras, collectibles) and pre-loved fashion. Specialty wins, mass market is conceded.
3. The $15–$22B Competitive Band
Tight mid-tier: Temu $22B (direct-from-China), TikTok Shop $15B (+68% YoY, content-first), Walmart $15B (200K+ sellers, 6× ads growth). Three different playbooks fighting in the same band.
4. Shopify — The Invisible Giant
Shopify holds 14% US e-commerce share without being a marketplace. Global GMV reached 66% of Amazon 3P GMV (2025). DTC stores aggregated rivals centralized marketplaces.
5. Specialized & Emerging Players
Curation beats breadth in verticals: Wayfair $10B (home goods), and the $6B tier — SHEIN (fast fashion), Etsy (handmade), Whatnot (live auctions). Defense against giants via niche depth.
Top US Marketplaces — by GMV (3P only)
Source: Marketplace PulseAmazon's $300B is 7.7× the #2 (eBay). The "tight mid-tier" between $15–$22B is the most contested band: Temu, TikTok Shop, Walmart. Sources: Marketplace Pulse, eBay Earnings, ECDB, Momentum Works, Etsy Earnings, eMarketer.