Amazon remains the dominant force on ecommerce marketplaces, but sellers are looking beyond the platform for growth. Social platforms are turning product discovery into purchases, adding new competitors to the marketplace mix. As the ecosystem expands, US retailers are courting shoppers abroad, and that global push is converging on one especially fierce battleground: Latin America.

This FAQ covers how marketplace power is distributed, where the growth is, and what sellers should do about it in 2026.

What is an ecommerce marketplace?

An ecommerce marketplace brings products from third-party sellers into a single platform, sometimes along the operator’s own inventory. The operator supplies the audience and payment infrastructure, and often adds fulfillment and advertising services. Amazon, Walmart Marketplace, Mercado Libre, and TikTok Shop all follow that basic model.

The model dominates online retail because it concentrates selection and demand: In 2026 the top 18 ecommerce retailers will drive 75.1% of total retail ecommerce sales in the US, per an EMARKETER forecast.

For brands, that concentration makes marketplaces both valuable and difficult to navigate. The largest platforms can deliver reach, convenience, and sales, but they also set the fees, control product visibility, and own much of the customer relationship. Success depends on choosing where marketplaces can add growth without eroding margins or weakening customer connections.

How dominant is Amazon among ecommerce marketplaces?

Amazon remains the gravitational center of US ecommerce, holding 39.7% of all US ecommerce sales in 2026, with no other retailer close, per EMARKETER.

That share underpins a second business: In 2026, Amazon will capture more than 79.4% of all US retail media digital ad spending, since advertisers follow transaction volume.

For sellers, that dominance creates both reach and dependency. Amazon can deliver sales at a scale that competitors cannot match, but the platform’s fees, advertising costs and control of customer data can pressure margins and limit customer relationships. Therefore, brands should treat Amazon as the anchor of a broader marketplace portfolio, then diversify across Walmart Marketplace, TikTok Shop, and category-specific platforms to pursue incremental growth and reduce their reliance on any single operator.

How are marketplaces expanding across borders?

Cross-border expansion is the marketplace battleground of 2026, with Mexico as the test case. Mercado Libre announced a $4.6 billion investment in Mexico for 2026, a 35.3% increase over the prior year and its largest annual commitment to the country. One day later, Walmart opened Walmart.com to international customers with Mexico as the first market, offering hundreds of thousands of US products with duties calculated at checkout.

The stakes: EMARKETER expects Mercado Libre to generate $17.87 billion in Mexican ecommerce sales in 2026, 25.5% of the country's retail ecommerce, with Amazon at $13.84 billion and 19.8%.

“When Mercado Libre committed $2.5 billion to Mexico in 2024, its goal was partly to stay ahead of Amazon and Asian platforms,” said Matteo Ceurvels, EMARKETER principal analyst for Latin America and Spain. “The 2026 commitment nearly doubles that figure, and its growing share of the market suggests the strategy is working.”

How are social platforms becoming marketplaces?

Social commerce has produced the fastest-growing marketplace in US retail. EMARKETER expects TikTok Shop to generate $23.41 billion in US sales in 2026, making it the fastest-growing retailer EMARKETER tracks for the second consecutive year, with an ecommerce business larger than Target, Kroger, Shein, and Best Buy, per a June 2026 EMARKETER forecast.

TikTok Shop's discovery-led model differs from search-led marketplaces: Purchases often begin with a creator on someone’s feed, not with a shopper typing into a search bar. Its success has pulled even multibrand retailers like Ulta and Sally Beauty onto the platform. This indicates the marketplace model is splitting into two architectures, search-based (Amazon, Walmart) and discovery-based (TikTok Shop), each requiring different seller capabilities.

What competitive pressures are reshaping marketplaces?

Marketplaces are feeling pressure from 3 different directions:

• Low-cost competitors are crossing borders. Shein, Temu, and Shopee are pushing into Latin America and other regions, forcing established players to defend their prices and their share of shoppers.
• Regulators are pushing back on aggressive promotions. Chinese authorities are scrutinizing sales tactics at Alibaba, Pinduoduo, JD.com, ByteDance, and Xiaohongshu amid weak domestic demand.
• Fast delivery requires heavy lifting. Mercado Libre plans to invest $4.6 billion in Mexico this year across technology, logistics, financial services, brand building, and 8,500 new hires. Same-day delivery already reaches 37 Mexican cities, showing how much infrastructure marketplace leaders must build to stay ahead.

These pressures feed one another. Low prices attract shoppers, fast delivery keeps them coming back, and sellers follow the demand. A marketplace that falls behind on price or convenience can quickly lose both sides of its business.

How should brands and sellers approach marketplaces in 2026?

Brands do not need to sell on every platform, but they should think carefully before relying on one. Give each chosen marketplace a clear role, then adapt assortment, content, and operations to the shoppers it serves.

• Anchor on Amazon, grow elsewhere. Amazon's reach remains difficult to match, but TikTok Shop's growth and Walmart's expansion reward early movers in secondary markets.
• Treat cross-border selling as localization, not just shipping. As Walmart.com opens to Mexican shoppers, eligible sellers should prepare Spanish-language listings and make duties, delivery times, and returns easy to understand.
• Match capabilities to architecture. Search-led marketplaces reward listing optimization and retail media; discovery-led marketplaces reward creator networks and content velocity.
• Keep pace with delivery expectations. Mercado Libre’s logistics investments could shorten fulfillment timelines in Mexico. Sellers should monitor those changes closely and ensure their marketplaces can meet the promises shown to shoppers.
• Count the cost of advertising as part of the cost of competing. On major marketplaces, paid placements increasingly determine which products shoppers see. Brands should weigh advertising, fees, and fulfillment costs together when judging whether a channel delivers profitable growth.

We prepared this article with the assistance of generative AI tools and stand behind its accuracy, quality, and originality.

EMARKETER forecast data was current at publication and may have changed. EMARKETER clients have access to up-to-date forecast data. To explore EMARKETER solutions, click here.