The United States policy established in the late 19th century and the early 20th century that
would allow for a system of trade in China open
to all countries equally.

Open door policy.

Explanation:

Open door policy refers to the United States policy established in the late 19th century and the early 20th century that would allow for a system of trade in China open to all countries equally. This policy was enunciated (proclaimed) by John Hay who was the secretary of state of the United States of America.

Basically, the open door policy sought to keep China open to trading with all other countries on an equal basis and without bias towards any of the imperial powers such as Germany, France, Britain, Japan and Russia. It prevented all of the aforementioned countries of being dominant or having a total control of the Chinese economy.

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