Don’t automatically assume that the off-brand case for your new iPhone 11 or the generic Halloween costume you just ordered from Amazon is being shipped from China. A new study by e-commerce analytics firm MarketPlace Pulse of the top 10,000 third-party sellers on Amazon.com revealed that US companies still dominate, though Chinese sellers account for more than a third of the marketplace. Just under half, or 47%, of the top Amazon.com sellers are based in the US, while 38% are based in China.

The success of Chinese sellers on Amazon can largely be attributed to the e-commerce giant’s Fulfillment by Amazon (FBA) service, which allows China-based merchants to use Amazon to pack and ship their products around the world using the same two-day Prime shipping as US sellers. China’s membership in the Universal Postal Union (UPU) also allows it ship packages globally at subsidized rates. Even if a Chinese seller elects not to use Amazon’s fulfillment service, they can still opt for a special category of first-class mail known as “ePacket” that allows them to ship to US customers at less costly rates.

The Trump administration had previously threatened to put an end to cheap China-to-US shipping by leaving the UPU, but last week the US reached an agreement with the international body that would allow it to remain in exchange for setting its own inbound postage rates. The US Postal Service was scheduled to leave the UPU on Oct. 17, which would have effectively ended the agreement that allowed Chinese businesses to ship items to the US at very little cost.

Outside of the US, China has an even tighter grip on the e-commerce giant, where it accounts for 40% of the top merchants. China makes up 34% of top sellers in the UK, 47% in France, 45% in Italy, and 52% in Spain according to a MarketPlace Pulse study from May. Even if business in the US were to grind to a halt, it’s unlikely China’s dominance of global e-commerce will be threatened any time soon.

That being said, more Amazon marketplace products were shipped from one zipcode in Brooklyn, New York, than any other single place, MarketPlace Pulse found. The 11219 zip code in the Borough Park neighborhood took top billing, and is home to a group of Orthodox Jews who have built a small empire selling products through Amazon, BuzzFeed recently reported.